Complete guide to understanding SMTP error codes. Learn what each error means and how to fix email delivery problems.
These errors are temporary. The server may accept the message if you retry later.
Server temporarily unavailable, try again later
Mailbox temporarily unavailable, often due to policy reasons
Server encountered a local processing error
Server ran out of storage space
Server cannot accept parameters at this time
These errors are permanent. The message will not be delivered without changes.
Command not recognized or syntax error
Invalid arguments or parameters
Server does not support this command
Commands sent in wrong order
Command parameter not supported
Server requires authentication before sending
Invalid username or password
User doesn't exist or mailbox unavailable
Recipient is not on this server
Email exceeds maximum allowed size
Email address format is invalid
General failure, often spam-related
Temporary failures. The server is telling you to try again later.
Permanent failures. You need to fix something before retrying.
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