How do ESPs handle auto-responses vs bounces?

Auto-responses and bounces require different handling:

Auto-response characteristics:

From a human mailbox, not MAILER-DAEMON. Contains "auto-reply," "out of office," "vacation" text. Often includes original message reference. No SMTP error codes.

Bounce characteristics:

From postmaster, MAILER-DAEMON, or null sender. Contains SMTP codes and DSN format. Indicates delivery failure. Structured according to RFC 3464.

Detection methods:

Check sender address patterns. Scan for auto-reply keywords. Look for DSN MIME structure. Analyze header indicators.

Why distinction matters:

Auto-responses should not trigger suppression. Bounces require classification and action. Misclassification causes list problems.

Auto-responses are friendly waves from the shore. Bounces are signals that the ship could not dock.