EMAIL LIST VALIDATION

The bulk email validator accepts .txt, .xls, .xlsx, and .csv file types. Please make sure your file is in one of our accepted formats. When you upload a file, our system will scan it. The file will be rejected if something unusual is detected. If you upload a .csv, .xls, or xlsx file, the first few columns will appear after you select the file you want to upload. Our system will try to determine the column's data type, as well. Any mistakes can be fixed before validation. If you can't get the system to accept your file, please use the help button on the bottom right to contact us.

Column matching is important, because if you upload a .csv, .xls, or .xlsx file with a first name column, our system will use that information to tell you the gender of that email. Apart from the gender, our system also has the ability to determine the location, account creation date, first and last name of some of the emails you upload. It will use the data you provide and fill in the gaps. We don't store your emails or your data. Our Data Append feature uses public sources of information known to be 99.6% accurate. If the IP address is provided, we will append the city, region/state, zip code, and the country to the output.

All duplicate, uni-coded, and malformed email addresses will be removed from the list. So, if you upload a list of 5,000 emails and you have 1,000 duplicates, only 4,000 will be processed. No, you will NOT be charged for submitting duplicate, uni-code, or malformed emails. Invalid email syntax is different from uni-coded and malformed emails. Once your file finishes processing, look to the right side and click the Expand Results arrow. This will expand and show if any of the mentioned conditions above were found.

ZeroBounce will truncate all file names over 70 characters. We do this because Windows will only support 160 characters in a file path and with log filenames customers hit that limitation when extracting the files from the zip file. Please name your files accordingly, to not exceed the 70 character limitation.

Popular email domain lists:

• 250,000 email addresses: Approximately 10 minutes or less
• 1 million email addresses: Approximately 45 minutes or less

Popular domain examples: Gmail, GSuite, Yahoo, Outlook, etc.

Mixed/uncommon/complex email domain lists:

• 250,000 email addresses: Approximately 2.3 hours or less
• 1 million email addresses: Approximately 5 hours or less

Processing time will vary based on the domain type, configuration complexity, and the number of attempts required to accurately verify the data.

ALLOWED FILE FORMATS

Allowed file formats:

• .txt
• .csv
• .xls
• .xlsx

Examples of Accepted Text File Formats:

Example Text File 1:

A TXT file that is separated with Comma's [ , ], Pipes [ | ], Tabs [ ], or Semi-Colons [ ; ] (without Carriage Returns and Line Feeds).

Example Text File 2:

A TXT File with only (Carriage Returns and Line Feeds).

Example Text File 3:

A TXT Files that looks like a CSV file will be converted to a CSV file when you upload it.

Examples of Accepted CSV File Formats:

A CSV file is accepted if it's separated by Comma's [ , ], Pipes [ | ], Tabs [ ], or Semi-Colons [ ; ]. If it's separated with a different delimiter, it will consider your CSV File as a single column file. If you save your spreadsheet as a CSV or TXT file, the system will accept it.

Example CSV File 1:

A typical accepted CSV file format

Example CSV File 1:

A typical accepted single column CSV file format

• If your CSV/XLS file contains a header row (in the column matching screen), please check the "Yes" , checkbox for "Does your first row contain labels?" before clicking "Next Step." - If you check "No," it will process the header row as an email address.
• If your CSV file has multiple columns of email addresses, we will allow you to select which column of emails you want us to process
• If we detect a large number of invalid emails or missing emails the system will reject it.
• All rows that don't have an email address in it will be ignored and removed.
• All duplicate emails will be removed, if a duplicate email is encountered the entire row is removed.
• If you have multiple email addresses in the same cell, it will be processed as a single email address, which will all end up being invalid
• We support up to 500 columns of data in your CSV file and a 1 gigabyte file size uploads. For large files, we recommend CSV and NOT XLS/XLSX (please convert/save as .csv).

Once your file finishes processing, click the purple Download button on the right side. The appearing window will ask you to select which properties you want us to append to your results. We break down your results into separate files based on the status of the email: Valid, Invalid, Catch-All, SpamTrap, Abuse, Do Not Mail, and Unknown (i.e. YOUR_UPLOADED_FILE_NAME_valid.csv, YOUR_UPLOADED_FILE_NAME_invalid.csv and so on). We will include the original uploaded file in the results as well. We compress all files into a .zip file. If you enabled password-protected downloads, we will encrypt the .zip file and email a password to you

Please visit our status codes documentation for a complete reference of all status and sub_status codes found in your downloaded files.

• _abuse.csv- This file contains all identified emails that are likely to mark your emails as spam.
• _all_results.csv- This file contains all the results.
• _catch_all.csv- This file contains all emails that our system identified as a catch-all domain. (catch-all domains are domains that accept any email, however, we do not recommend to sending to catch-all domains because it's risky and can harm your IP reputationⓘ)
• _donotmail.csv- This file contains all emails that are role-based, disposable, toxic, and possible spam trap email addresses and shouldn't be mailed to, look at the sub_status to determine the classification.
• _invalid.csv- This file contains all emails that we identified as invalid.
• _original.csv- This is the original file you uploaded.
• _overview.pdf- This PDF contains of an executive summary of your results.
• _spamtrap.csv- This file contains all emails that we identified as being spam traps.
• _unknown.csv- This file contains all emails that we could not verify, this normally happens when the email server in question times-out or responds with a non RFC-compliant response.
• _valid.csv- This file contains all the valid email addresses you should mail to.
• _rejected.csv- This file contains all emails/rows that we rejected and didn't process, don't worry you weren't charged for these. We will reject duplicate emails, malformed emails, missing emails, and emails with non-ASCII characters. If this file does not appear in your download, nothing was rejected. You can see the counts of what was rejected by clicking the arrow next to the download button of the validated file.

When you download your results, it will be downloaded as an encrypted zip file, the password for the file will be sent to the email account you registered with. Please allow a few minutes for the password to arrive and make sure you check your spam/junk folders. If you do find it in your spam/junk folder, please mark it as "NOT SPAM" , so it will land in your inbox on any new downloads.

Please note that every time you download the file, even the same file, it will have a different password.

We do this as an additional step in protecting your data. For example, if someone gains access to your ZeroBounce account, they won't be able to decrypt your data without also having access to your email.

Analyzing your results

Have you just downloaded your email validation results and need help interpreting them? We’re here to help.

Once you have downloaded and unlocked your ZIP file, you will find up to 11 files in CSV format and 1 file as PDF:

In the CSV files, you will find 13 additional columns in the first row.

Example Results Output

Need more help analyzing your email verification results? Reach out – our team is here for you 24/7 to answer questions and guide you.

• Valid - We determined these addresses to be valid and safe to email. They will have a very low bounce rate of under 2%.
  If you receive bounces, it can be because your IP might be blacklisted where our IP was not. Sometimes, the email accounts exist, but they only accept mail from people in their contact lists. In other instances, you may be throttled on the number of emails you can send to a specific domain per hour. It's important to look at the SMTP Bounce codes to determine why a bounce occurred.
  • Alias_address - (valid) These email addresses act as forwarders/aliases and are not real inboxes.
    For example, if you email “forward@example.com,” your email is forwarded to “realinbox@example.com.”
    An alias is a valid email address, and your email will not bounce. This status aims to provide more information about the email address. We can sometimes detect alias email addresses, and when we do, we let you know.
  • Leading_period_removed - (valid) If a valid gmail.com email address starts with a period, '.', we will remove it so that the email address is compatible with all mailing systems.
  • Alternate - (valid) These emails are valid but likely to be secondary addresses for the users. Alternate emails are often used to sign up for accounts but do not see much engagement.
    Unlike primary email addresses, which look more formal, alternate emails usually contain numbers or special characters, e.g. 12j.o-hn2023@gmail.com. Identifying alternate email addresses allows for better email list segmentation. Users with formal emails are more likely to engage with your content.
  • accept_all - (valid) These addresses belong to domains on the ZeroBounce accept_all list. The destination mail server is configured to accept any recipient and never issue an SMTP bounce (e.g., amazon.com, zerobounce.net). Because long-term sending data shows an exceptionally low bounce rate (< 2 %), we treat them as Valid while flagging them with the accept_all sub-status so you can segmentor monitor engagement if desired.
  How is this different from the standalone “Catch-all” status?
  • accept_all ➜ Domain vetted by ZeroBounce, historically delivers, returned as valid;
  • Catch-all ➜ Domain not in the allow-list; actual deliverability cannot be confirmed;
• Invalid - These are the emails that we determined to be invalid. Please delete them from your email list. The email can be deemed invalid for various reasons, such as “mailbox not found.” The address also may not accept emails.Below is a list of sub_status codes to help explain some of the invalid results.
  • Does_not_accept_mail - (invalid) These domains only send mail and don't accept it.
  • Failed_syntax_check - (invalid) Emails that fail RFC syntax protocols.
  • Possible_typo - (invalid) These are emails belonging to commonly misspelled popular domains.
  • Mailbox_not_found - (invalid) These emails addresses are valid in syntax, but do not exist.
  • No_dns_entries - (invalid) These emails are valid in syntax, but the domain doesn't have any DNS records or incomplete DNS Records. Therefore, mail programs will have difficulty delivering emails to them or be entirely unsuccessful.
  • Mailbox_quota_exceeded - (invalid) These addresses exceeded their space quota and no longer accept emails (temporarily).
  • Unroutable_ip_address - (invalid) These email domains point to an unroutable IP address.
• Catch-all - These emails are impossible to validate without sending a real email and waiting for a bounce. “Catch-all” means that the email server tells you that the email is valid, whether it's valid or invalid. If you want to email these addresses, we suggest you segment them into a catch-all group with the knowledge that some of your emails will bounce.
  Learn more about Catch-All Emailsⓘ
• Spamtrap - These emails are believed to be spam traps, and you should not email them. We have the technology to determine if certain emails should be classified as spam traps. We don't know all the spam trap email addresses, but we know many of them.
  Read our Guide to Spam Traps to learn more.
• Abuse - These emails are of people known to click the abuse links in emails, hence abusers or complainers. We recommend not emailing these addresses.
• Do_not_mail - These are company emails, role-based, or simply addresses you should avoid emailing. They are broken down into 6 sub-categories "disposable," "toxic," "role_based," "role_based_catch_all," "global_suppression," and "possible_trap." Examine this file and determine if you want to email these addresses. They are valid email addresses but shouldn't be mailed in most cases.
  • Global_suppression - (do_not_mail) These emails are found in many popular global suppression lists (GSL). They consist of known ISP complainers, direct complainers, purchased addresses, domains that don't send mail, and known litigators.
  • Possible_trap - (do_not_mail) These emails contain keywords that might correlate to possible spam traps like spam@ or @spamtrap.com. Examine these before deciding whether to send emails to them or not.
  • Role_based - (do_not_mail) These emails belong to a position or a group of people, like sales@ info@ and contact@. Role-based emails strongly correlate to people reporting emails sent to them as spam and abuse.
  • disposable- (do_not_mail) These email addresses are temporary and become invalid after a set period. Avoid adding disposable emailsⓘ to your list to avoid future bounces.
  • toxic- (do_not_mail) These email addresses are known for abuse and spam. They may also be bot-created emails. If any of your emails possess this flag, you shouldn't email them. We also provide additional fields that you should consider before emailing.
  • Role_based_catch_all - (do_not_mail) These emails are role-based and belong to a catch_all domain.
  • mx_forward - (do_not_mail) These emails belong to domains set up to forward their MX records into one domain. Their use case is somewhat similar to disposable domains.
• Unknown- We couldn’t validate for one reason or another. Typical cases include an offline mail server or an anti-spam email system.
  In most cases, 80% of unknowns are invalid/bad email addresses. We have the lowest "unknowns" of any email validator and don't make this statement lightly. We paid and tested email lists at over 50 validation companies to compare results.
  If you do encounter a large number of unknowns, please submit those for re-validation. Remember, you are not charged for unknown results, credits will be credited back. If you still have a large number, contact us and we will take a look and verify.
  • Antispam_system - (unknown) These emails have anti-spam systems deployed that are preventing us from validating these emails. You can submit these to us through the contact us screen.
  • Exception_occurred - (unknown) These emails caused an exception when validating. If this happens repeatedly, please let us know.
  • Failed_smtp_connection - (unknown) These emails belong to a mail server that won't allow an SMTP connection. Most of the time, these emails will end up being invalid.
  • Forcible_disconnect - (unknown) These emails belong to a mail server that disconnects immediately upon connecting. Most of the time, these emails will end up being invalid.
  • Greylisted - (unknown) Greylisting technology is temporarily preventing the validation attempt. If you resubmit these emails, they will often validate on a second pass.
  • Mail_server_did_not_respond - (unknown) These emails belong to a mail server that is not responding to mail commands. Most of the time, these emails will end up being invalid.
  • Mail_server_temporary_error - (unknown) These emails belong to a mail server returning a temporary error. Most of the time, these emails will end up being invalid.
  • Timeout_exceeded - (unknown) These emails belong to a mail server that responds slowly. Most of the time, these emails will end up being invalid.

We also provide a sub_status code to help explain some of the unknown and invalid results. Not all unknowns and invalids will have sub_status codes.

• free_email- [true/false] Does the email come from a free provider?
• mx_found- [true/false] Does the domain have an MX record?
• mx_record- The preferred MX record of the domain
• smtp_provider- The SMTP Provider of the email or [null] (BETA)

As a responsible email validation service, we do our best to protect your IP/Domain Mailing Reputation. Your mailing campaign succeeds when your email lands in the inbox, not the junk box.

The "Do Not Mail" Status represents one of the next steps where we identify potential emails that can cause harm to your IP/Domain Reputation.

• MailChimp
• Constant_Contact
• SendGrid
• Nation_Builder
• Benchmark_Email
• Port_25

Let's dig a little deeper into the meaning of role-based and why, but let's hear it from the mailing exports of major ESP Providers who send billions of emails daily. Click on the following links below.

There are hundreds of more links from many more large companies than the ones above explaining why. We understand that depending on your business model and industry, you might need to send messages to role-based emails. You may do this, but we must communicate the risk involved. It's your decision on which role-based emails to mail and whether the risk is worthwhile.

All emails that we flag as "Role-Based" are valid emails.

Below is an example of the PDF that will be included in your zip file.

This Report is broken into a few sub-sections:

• Top Domains - This shows you the top 10 domains found in your email list and breaks it down by percentages. Thus you can get a better picture of the different domains in your database and plan your marketing activities accordingly.
• Validation Results - This gives you the overall statistics of the different email validationⓘ results of your entire file. You can see exactly how many emails in your list were valid, invalid, spam traps, catch-all, unknown or abuse (complainers).
• Data Appends - This shows you how successful we were in appending additional data to your email list. For some of your contacts, our email checker will add the subscriber’s first and last name, gender, location and age of the email address.
• IP Location Data Appends - If you uploaded the IP addresses along with your emails, the report will show you demographics by top countries and top regions/states.

Executive Report

Do you have any questions about your email verification report? Our team can help – reach out to us anytime, we are available 24/7.

We are not a storage company and our team is extremely passionate about data protection. From day one, we wanted to make sure your data is secure while you use our email list validator.

ZeroBounce uses complex mechanisms to protect your data and employs military-grade protocols to safeguard it.

We will store your email validation results up to 30 days, and then we will delete them automatically. By default, you will be notified by email when your files will be deleted in 7 and 2 days, respectively. You can turn off these notifications in your notification settings, as seen below.

To access your notification settings, access your "Profile" on the top-right menu. Then, click or scroll down to “Notification Settings”. Don’t forget to click the Save button below these settings if you made any modifications. "

Notification Settings under Profile

Of course, you can delete your own files from our system at any time.

We do encrypt the files you upload and download. We do not store your data in our database, just the summary data you see in the “Validate” section.

Your data is your data, and we take safeguarding that data very seriously. Once the files are deleted, either automatically or by you, that summary data is also deleted.

Need more information about how to delete your data? Our team can help – reach out, we’re available 24/7.

Thousands of customers around the world enjoy using our email checker. However, email validation is a complex field. A lot goes into ensuring an email address is valid and active, so errors can occur.

We’ve always worked with you to make ZeroBounce better and we continue to value your feedback. Have you noticed anything strange while using our email list cleaningⓘ service?

We’d appreciate it if you let us know.

For instance, if we mark an email as "Invalid" and you know it is "Valid", we would like to know about it.

Also, if you get an unusually high bounce rate – such as higher than 2% – for emails we’ve marked “valid,” we would like to know about that, also.

Please email us at support@zerobounce.net with the SMTP logs. It's very important that we see the actual SMTP Reply, because emails can bounce for many different reasons, including the content of the email you are sending.

We are always trying to improve our algorithms, and we believe we offer the best validation, abuse and spam trap detectionⓘ, and data append features on the market.

Your feedback and suggestions have been of great help so far, so please don’t hesitate to contact our 24/7 customer support team.

• Q:What is Greylisting?
  A:Greylisting is an anti-spam technology deployed by mail servers to prevent spam. The receiving mail server tells the sender to please retry to send the email again in X minutes.

  A well-configured mail server will attempt to resend an email on different intervals, until it's accepted or rejected by the receiving mail server.

  There are many types of greylisting, but the most common one is time-based greylisting, as mentioned above. Each mail server has a different time they greylist the sender for, per email, normally between 1 and 20 minutes.

  ZeroBounce deploys break-through anti greylisting technology.

  When we encounter any greylisting, we will wait 20 minutes and retry to validate those specific emails. This reduces the number of "Unknowns" you will receive back from us. So, you wait a little longer for your results, but your results will be a lot better. It’s worth noting that ZeroBounce will not charge you for the “Unknown” results.

  It doesn't matter how many greylisted email addresses you upload to be validated. Whether it's 1 or 100,000, the processing is only delayed by 15 minutes in total.

Other companies say it, we put it in writing. ZeroBounce, the leader in email validation, makes you the promise of cleaner and safer email lists. We guarantee the following accuracy rates at a minimum:

• 96%+ Accuracy rates on AOL, Yahoo, and office 365 email accounts. This does not include disabled accounts.
• 99.6% Accuracy rates on everything else.

How the Guarantee works:

If the accuracy rates are below these thresholds, we will refund 5 times the amount for each 1%. Let's say you have a 97% accuracy rate, which is 1% below the guaranteed threshold of (99.6% Accuracy rates on everything else). We will refund 5 x 1% (or 5%) of your total validation cost for those emails. If your accuracy rate is 2% below the guaranteed threshold, our refund will be of 10% of your costs. If it's 4% below, the refund will be 20%, and so on.

In order to qualify for the guarantee, the following conditions must be met:

• You only email the _valid.csv and remove all toxic and disposable emailsⓘ.
• You email the list within 72 hours after cleaning.
• Bounces must be invalid emails (Hard Bounces).
• Bounces due to spam content, blacklisted IP's, technical Issues, invalid mail configuration, throttling, etc do not qualify for the guarantee.
• The minimum list size must be 1000 emails.
• This list must be an opt-in list that you collected and not purchased from a 3rd party
• You must provide an export of your full mailing of all emails you sent to and their bounce responses (the actual SMTP Codes and messages of the bounces), not your email sender classifying it as a bounce. ZeroBounce does not guarantee the acceptance of your cleaned list at any ESP provider.

In order to determine why the emails that were sent bounced, it's important to have access to these codes, so you can make adjustments and decisions to remedy the issue.

Below you will find a summary of codes, keep in mind, there are thousands more, depending on the mail server the same codes will have different meanings, these are just a few examples.

Reference: RFC2821

The ZeroBounce email validator allows users to create custom filters to allow or block emails, email domains, specific mx records or TLD (Top Level Domain). Making these allowlists and blocklists will enable you to customize your email validation experience for your needs.

Creating these custom filters simplifies email validationⓘ by automatically allowing or blocking values and improve email list validation efficiency.

To create your email validationⓘ rules, sign in to your ZeroBounce account and visit your account settings.

In the settings, you’ll find two mandatory dropdown fields. You must select a value for both to create a new rule successfully.

Important Note - Before you begin, know that more specific rules will take priority over less specific ones.

For example:

Rule 1: Block - Email - test@example.com

Rule 2: Allow - Domain - example.com

If you need to edit an existing rule, you can do so by locating the rule in your list and clicking Modify.

Doing so will prompt your rule to appear in the customization field above. You can then switch your rule from Allow to Block or vice versa.

If you wish to edit the Target or Value, delete the rule from your list and create a new one. You can do this by clicking Delete. A confirmation screen will appear to help prevent accidental rule changes on your account.

Then, you may create a new rule that contains the proper Rule, Target and Value.

If you experience issues creating your custom allow or block rules, please contact the ZeroBounce support team - available 24/7 via phone, email or live chat.

It primarily impacts disabled Yahoo, AOL, Verizon and Catch-all email addresses. Opting to use it increases the accuracy of the validation results on these domains to 99.9%

When Verify+ is enabled on your account or list, ZeroBounce automatically performs an extra step called Catch‑all Email Validation. This step runs only if there are at least 10 catch-all emails identified in the initial validation (phase one). Its goal is to reduce the number of unresolved catch‑alls by applying deeper models and additional signals.

How it works

• Trigger: After Phase 1 (Bulk Validation) is completed, if your results include at least 10 catch-all addresses, we proceed to Phase 2: Catch-all Email Validation for those addresses.

• Progress: You’ll see a progress card in the results. During processing, it shows a status message (“Analyzing your catch‑all emails… This process can take up to 48 hours to complete.”).

• Results: When complete, some catch‑alls may become Valid or Invalid; the remainder will stay Catch‑all.

Where you’ll see it in the UI

• Results page → Phase 2: Email Validation Catch‑All panel with the donut chart

• You can download the results once Phase 2 is complete to obtain the latest classifications.

How to disable it

You have the option to disable the Catch‑all Email Validationⓘ feature by deselecting the corresponding checkbox in the final pop-up during the file upload process. Once deselected, the uploaded file will not proceed to Phase 2, and catch‑all addresses will not undergo additional validation.

Catch-All Validation Notes & FAQs

Disclaimer: Catch-all domains are among the most challenging to validate, as they often use multiple layers of filtering (sometimes three or four). These filters can occasionally affect validation accuracy, leading to slightly less reliable results. Always exercise caution when sending to addresses marked as valid after Catch-All Verification.

• Scope: To reduce the number of unresolved catch‑alls.

• Timeline: Processing may take up to 48 hours, depending on list size and domain behavior.

• Data privacy: All processing is performed in‑house; we do not share your data with third parties.

Tip:

Keep Verify+ enabled for your lists to automatically benefit from Catch‑all Email Validationⓘ without any extra steps.