Hannah Schroeter wrote:
I don't like those semantic games like calling .forward style
It's shorter than the official STD 10 definitions of 251 + 551:
251 User not local; will forward to <forward-path>
This reply indicates that the receiver-SMTP knows the user's
mailbox is on another host and indicates the correct
forward-path to use in the future. Note that either the
host or user or both may be different. The receiver takes
responsibility for delivering the message.
551 User not local; please try <forward-path>
You're responsible, otherwise you can reject it with error 551.