things as bad as:
HELO mailhost.domain.tld
MAIL FROM: <user(_at_)domain(_dot_)tld>
RCPT TO: <user(_at_)domain(_dot_)tld>
DATA
...
Reply-to: user(_at_)domain(_dot_)tld
Errors-to: user(_at_)domain(_dot_)tld
From: user(_at_)domain(_dot_)tld
To: user(_at_)domain(_dot_)tld
Subject: Otheruser(_at_)otherdomain has send you an e-card
...
And we should prevent giving folk like this some pain because???