Email Bounce Types • Library - Connected

Quoted on this wiki

Every place a page here uses this source, in the order the words come in it.

1. Real-time validation at signup catches problems immediately: “Syntax checking (is this a valid email format?)” MX record verification (does this domain accept email?)

   In Email address validation

2. Syntax checking (is this a valid email format?) “MX record verification (does this domain accept email?)” Disposable email detection (is this a throwaway address?)

   In Email address validation

3. 5xx codes (Hard bounces): Permanent failures. Stop trying. “4xx codes (Soft bounces): Temporary failures. Try again later.” This distinction drives everything else.

   In Soft-bounce retry policies

4. Message too large (552 4.3.1): Your message exceeds the server's size limit. The only fix is a smaller message. “The correct response is automatic retry with exponential backoff:” Wait 15 minutes, try again

   In Soft-bounce retry policies