| Session-transcript | Other specifics | Explanation |
|---|
>>> RCPT To:<recipient's-address>
>>> 550 <recipient's-address>... User unknown
550 <recipient's-address>... User unknown
| -- | Recipient on the To: line is misspelled, or no longer has an account at that address |
550 <recipient's-address>...
Host unknown (Name server:
recipient's-host: host not found)
| -- | Recipient's host-name on the To: line is misspelled, or its name-server is down |
>>> MAIL From:<sender's address>
>>> 550 Access denied
...followed by one of three reasons at the right ---> | 550 Sorry, no access for this ip | Sender is from a known SPAM IP-address |
550 Sorry, no access for this domain | Sender is in a known SPAM domain |
550 Sorry, no access for this user | Sender is a known SPAMmer |
550 /directory-path/.forward: line 1:
(contents of line 1) ... Can't create output:
Permission denied
| -- | The recipient has a .forward file containing an unreadable address |
>>> DATA
>>> 553 user address required
> 554 <recipient's-address>... Service unavailable
or
451 From:domain must resolve
| -- | To: or From: line has an improperly constructed address. |
553 <recipient's-address>
... unauthorized relay traffic prohibited
554 <recipient's-address>
... Service unavailable
| -- | Sender is relaying mail -- probably using a commercial ISP while using a UM From:-address |
554 sendall: too many hops 19 (17 max)
(the numbers may vary, and addresses may be included) | -- | There is a mail loop -- probably the recipient has mail forwarded to another account, which has mail forwarded back to the original account |
>>> 553 Header Error
554 recipient's-address... Service unavailable
| -- | This can be pretty obscure. There is a non-parseable line in the header, but finding it can be difficult. One example:
Resent-Message-ID:
>"s3rGDD.A.saG.tTjM1"@earth.mat.net>
where a more standard message-id might look like this:
Message-Id:
>3.0.5.32.19980413115110.0082e9a0@tir.com> |
>>> DATA
>>> 553 Header Error 2
554 recipient's-address... Service unavailable
| -- | This "Error 2" may be a non-standard patch by the local postmaster to stop certain mail (e.g., used here to stop all messages with "Hi" in the subject line during a mass-mail battle) |
