肖建彬的博客

作者: 肖建彬 | 可以转载, 转载时务必以超链接形式标明文章原始出处和作者信息及版权声明
网址：http://www.xiaojb.com/archives/mailtech/null_smtp_clien.shtml

/dev/rob0 wrote:

This is slightly OT, sorry. Probably none of us like to be rejected. I
have an old (circa 2003) install of nullmailer who used to relay to
qmail, which never rejected anything it sent. Happy nullmailer.

The nullmailer sends mail from an internal-only Web form which appends
@domain, and, sadly, is not able to validate addresses. So if a user
mistypes his/her username (or puts in user@domain) nullmailer sends to
a bad address.

Quite some time back the nullmailer relay was changed to Postfix, and
the bad addresses are rejected, of course. Sad nullmailer. But it
doesn't take "go away" for an answer; it keeps trying with all the
rejected mails. Recently a slew of these were queued, filling the log
partition and causing a DoS.

Is there a null SMTP client which would deliver rejected mail to a dead
letter box and remove it from the queue?

Wietse Venema’s answer:

Instead of having the SMTP server reject all non-existent recipients,
as in:

   /etc/postfix/main.cf:
       smtpd_reject_unlisted_recipient = yes

You could exempt some clients:

   /etc/postfix/main.cf:
       smtpd_reject_unlisted_recipient = no
       smtpd_mumble_restrictions =
           ... check_client_access ... reject_unlisted_recipient ...

Or even:

   /etc/postfix/main.cf:
       smtpd_reject_unlisted_recipient = no
       smtpd_mumble_restrictions =
           ... permit_mynetworks ... reject_unlisted_recipient ...

This may be more convenient than replacing the nullclient.