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A bounced email is one that has been rejected by a receiving email server, which can happen for a number of reasons.
Bounces have a bounce notification and a bounce category provided by the inbox provider that contain information on why the email bounced. These reasons can range from bad-mailbox, indicating that the email address does not exist, to spam-related, indicating that the recipient email provider feels that the message is spam due to either its content or the reputation of the IP or domain sending it.
When an email is sent from Mixpanel and it bounces, a "Message Bounced" Event will be sent to your project and "Bounce Category" and "Bounce Notification" user profile properties will be set on the user's profile.
There are generally two types of bounces, hard and soft. Soft bounces are emails that are rejected for temporary or non-specific reasons, while hard bounces indicate that one should never try to send to that email again.
This is a permanent delivery issue. Mixpanel will exclude profiles with these Bounce Category properties from future emails.
Hard bounce categories:
- Bad-domain: the domain of the email address (for example '@gmail.com') is not valid
- Bad-mailbox: the email address doesn’t exist on the server
- Inactive-mailbox: the email address used to exist but has become deactivated
- Invalid-sender: the receiving domain does not like the IP or domain sending the email
- Policy-related: a catch-all category, often indicating the sender is on a blacklist
- Relaying-issues: the mail is being relayed and errors out
- Routing-errors: the mail is being routed and there are fatal errors
- Spam-related: the receiving mail provider believes either the content or sender of this content is a spammer.
This is not a permanent delivery issue. Mixpanel will continue to send profiles with these Bounce Category properties future emails.
Soft bounce categories:
- Message-expired: the email was sent before the maximum time window allowed, after previous delivery attempts failed
- No-answer-from-host: there was no response from the recipient's server
- Other: the email was rejected for other reasons
- Quota-issues: the recipient's mailbox exceeded the email limit
- Bad-configuration: the recipient’s server is not allowing new emails
- Bad-connection: there is an error with the remote server
- Content-related: the email’s content caused the bounce
- Protocol-errors: there are syntax errors in the SMTP protocol on the recipient’s server
- Virus-related: there are corrupted emails