Hard bounce reason

Explanation

Email address does not exist

Email address doesn't exist for the contact to whom you sent the campaign.

Domain name does not exist

If your contact uses an email address with a specific domain name instead of using gmail or yahoomail, it doesn't exist.

Recipient email address is invalid or malformed

If the email address of your contact isn't specified correctly or has mistakes, this happens.

Recipient email server has permanently blocked delivery

The email server used by your recipient has blocked emails from the domain you use for sending campaigns.

Email address was deleted or deactivated

Recipient's email address isn't active anymore.

Rejected due to policy restrictions

Due to certain policies placed on the recipient's server, your emails got rejected.

User unknown on the recipient server

Recipient's mail server doesn't know the mailbox or email address to which the email is sent.

Soft bounce reason

Explanation

Solution

Mailbox is full (over quota)

Recipient's inbox storage is full

You can request the recipient to clear storage space of their inbox or you can wait for some time and retry later.

Mailbox is temporarily disabled or inactive

Account is inactive or suspended

This means the recipient's email account is inactive or suspended. You can notify them to reactivate the account or retry later.

Recipient server is down or offline

Mail server is unreachable

The recipient's mail server is down or cannot be reached. Retry will happen automatically; you can inform the recipient's IT team to flag this issue.

Too many messages sent in a short time (rate-limiting)

Sender triggered the recipient's rate limits

If you send too many emails in a short time, this will happen. You can warm up your IP or retry sending after some time. You can also batch send the emails.

Email message is too large

Exceeds allowed message size (e.g., >25MB)

This occurs if your email is too large due to large attachments like images, files, videos. We recommend you compress them or remove unnecessary attachments. You can also upload the files in file hosting software like Zoho WorkDrive and use links to share these files.

Temporary DNS issue

DNS record for the recipient domain is unreachable

Due to issues in the DNS record of the recipient's domain, this will happen. You can retry sending the email later. Request your contact to use a reliable DNS resolver to pinpoint the problem and resolve it.

Email blocked due to message content

Spammy keywords or suspicious links

This happens if the content of your campaign triggers the anti-spam filters of your recipient's email server. Please avoid using spammy words, URL shorteners, and suspicious links. You can check here for further information.

Fails DMARC / SPF / DKIM checks

Email failed authentication check

The recipient's mail server tested your campaign's authentication and the tests failed due to improper domain authentication from your end. Ensure SPF, DKIM, and DMARC are all published properly.

Rejected due to anti-spam filters

Message flagged by spam protection

The anti-spam filters of your recipient's email server has rejected your email. To resolve this, you can improve your domain reputation, avoid spammy content, and authenticate your sender domain.

Rejected due to anti-virus filters

Attachments flagged as malicious

This can happen if any files you've attached in your campaigns are deemed to be unsafe. Remove unsafe files; scan with antivirus before sending.

Doesn't meet recipient server's sender policies

Sender not allowed based on recipient server rules

Certain policies set by the recipient's email server can prevent your emails from reaching your recipient. You should contact the recipient's IT team to review bounce message and request allow listing.

Email cannot be relayed at the moment

SMTP relay denied for this message

This error occurs if the SMTP server you used to relay the email has rejected the relay. You must check the SMTP server's configuration to see if everything's configured properly. Contact the recipient admin if there's nothing wrong at your end.

Grey listing

Server delays the unknown sender’s first message

Since the recipient's email server thinks that the email it received is from an unknown sender, it can delay the receipt of the email. Retry will happen automatically. You can maintain an uniform and consistent IP for sending emails.

Connection timeout or temporary network issue

Network problem prevented delivery

This can happen if there's an issue with your network or firewall status. You can retry later after checking for issues with your network or firewall.

Etimeout issue

SMTP timeout occurred

If the SMTP server you use for relaying emails has a short timeout setting, this bounce can occur. We request you to increase the SMTP timeout setting and check its responsiveness.

Delivered time expired

Delivery wasn't completed within the retry window

You must ensure timely retry attempts and fix network or server issues.