Email Bounce Category Definitions

A bounced email is one that has been rejected by a receiving email server, which can happen for a number of reasons.

Bounces have associated with them both a bounce notification and a bounce category which have 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 a "Bounce Category" user property will be automatically set on the user's profile.

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There are generally two types of bounces, hard and soft. Soft bounces are emails that are rejected for temporary delivery reasons such as a sending rate limit has been reached, while hard bounces indicate that one should never try to send to that email again for reasons such as the email address being incorrect.

Hard Bounce

This is a permanent delivery issue. Mixpanel will not re-try delivery.

Hard bounces happen when:

  • 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: that the receiving domain does not like the ip/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.

Soft Bounce

This is not a permanent delivery issue. Mixpanel will re-try delivery. 

Soft bounces happen when:

  • 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.

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