Hello friends of Exim!
I recently upgraded from Exim 3.36 to Exim 4.20 (on Red Hat Linux 9)
and noticed a strange behaviour.
I'm connected with ISDN (64 kbit/s), and if the utilization of the
line is very high, Exim sometimes silently drops incoming connections
upon connect. No entry to the logfile (mainlog) is made, no SMTP
response code is given. I don't even get the typical log entry
"SMTP connection from [1.2.3.4]:4711 (TCP/IP connection count = 1)".
If I do a telnet to my mail server from the Internet, it looks like
this:
$ telnet my.mail.server 25
Trying 1.2.3.4...
Connected to my.mail.server.
Escape character is '^]'.
[...
Connection closed by foreign host.
$
I have ACLs for "acl_smtp_data" and "acl_smtp_rcpt" but not for
"acl_smtp_connect". I've also not set "host_reject_connection".
Setting "host_lookup" to "!*" won't fix the problem.
I've set "log_selector" to "+all". According to the source (smtp_in.c),
all failures either result in a logfile entry or in an SMTP answer (or
both ;-). But I get none of them.
If Exim drops the connection, it usually happens within the first
about 5 seconds after the connection has been initiated from the
outside world (Internet).
The whole thing looks like some kind of timeout. Maybe a failed DNS
lookup. However, even with host_lookup = !*" it fails.
But I've no idea, what goes wrong. I cannot remember to have had this
problem with Exim 3.36, and other applications behave well (their
responses are slow but they never drop a connection).
However, once the SMTP connection has been established, Exim won't
drop the connection (even on high bandwidth load).
Does anyone have an idea?
Greetings, Andreas
