What the error means.
WHAT A BOUNCE IS
A message telling you delivery failed.
THE TWO KINDS
Hard bounce: permanent. The address does not exist.
Soft bounce: temporary. A full mailbox, or a server unavailable.
WHAT TO DO ABOUT EACH
Hard: remove the address
Soft: it may deliver later
WHAT THE ERROR TEXT TELLS YOU
Frequently the exact reason.
COMMON REASONS
No such user Mailbox full Message too large Rejected as spam Sender not authorised Blacklisted
FOR "SENDER NOT AUTHORISED"
An SPF problem.
FOR "REJECTED AS SPAM"
Reputation or content.
FOR BLACKLIST REFERENCES
The message usually names the list.
WHAT TO DO
Read the actual text rather than assuming.
It frequently states precisely what is wrong.
WHAT TO SEND US
The full bounce message, not a summary.
THE FULL TEXT MATTERS
Details are in the parts people trim.
