On Sat, 22 Jan 2005, Richard Welty wrote:
> > The smtp fixup option on the Cisco's, (if enabled), is prone to causing
> > various problems with smtp. It may not be the cause, but it usually is
> > worth checking.
>
> if it's turned on, it will without question prevent esmtp from
> working. various other things break as well.
>
> to test, from outside, telnet to port 25 on the mail server. if the
> banner is mostly obscured with ***, then you need to turn smtp fixup
> off.
Indeed.
But this seems not to be the only cause of problems. There are some
aggressive configurations which filter out the ICMP packets that are
needed for MTU discovery. Depending on your particular TCP stack,
this can cause various strange effects. For example, short mails
which go through, while longer mails seem to proceed almost to
completion, hang for a long time, then time-out and retry, with the
cycle repeating indefinitely. See
http://www.exim.org/exim-html-4.40/doc/html/FAQ_0.html#TOC17
and previous discussions on this list.
