sendmail and hosts_access(5)

[Giorgos Keramidas]

On 2006-09-13 17:56, Matthew Seaman <m.seaman at infracaninophile.co.uk> wrote:
> hosts.allow triggers special behaviour with sendmail.  Unlike other
> services which just close the connection immediately, with sendmail
> what happens is that it will accept the connection, let the sender
> attempt to send e-mail, but then respond with a 500 'permanent
> failure' code.
>
> The reason for that is fairly simple: if a MTA gets no answer when
> trying to connect to a server and deliver e-mail, then the standards
> say it should requeue the message and try again for up to 5 days.  The
> only way to get the sending MTA to give up immediately is to issue a
> SMTP 500 error code.

Ah!  I see now.

Thanks for taking the time to write this cool, detailed explanation.

Now I know one more thing about Sendmail :-)