> rfc 2821 specifically forbids this behaviour.

quoted text
>

> 

> The DATA command can fail at only two points in the protocol exchange:

>

>    -  If there was no MAIL, or no RCPT, command, or all such commands

>       were rejected, the server MAY return a "command out of sequence"

>       (503) or "no valid recipients" (554) reply in response to the DATA

>       command.  If one of those replies (or any other 5yz reply) is

>       received, the client MUST NOT send the message data; more

>       generally, message data MUST NOT be sent unless a 354 reply is

>       received.

>

>    -  If the verb is initially accepted and the 354 reply issued, the

>       DATA command should fail only if the mail transaction was

>       incomplete (for example, no recipients), or if resources were

>       unavailable (including, of course, the server unexpectedly

>       becoming unavailable), or if the server determines that the

>       message should be rejected for policy or other reasons.

and that paragraph says right there, the server can decide it doesn't

have the resources to deal with it. no problem.  The RFC does not

forbid it
and 821 (which ain't dead yet) allows explicitly in the state transactions.

2821 is simply vague. 
-Bob