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Why 40-second delay in sending mail to SMTP server?

From Steve Snyder on Sat, 05 Dec 1998

On my LAN, when my (Win95- and OS/2-based) mail clients retrieve mail from my (RedHat v4.2) Linux server, it is all but instant. When sending mail to the server, there is a 40 - 45 second delay before the sent mail is accepted. Mail retrieval by the clients are done via POP3; mail is sent via SMTP.

Sounds like attempts at reverse DNS and/or 'ident'

These are the relevant lines from my /var/log/maillog. These lines are the result of sending mail from mercury.snyder.net (client running OS/2) to solar.snyder.net (server running Linux). Note that the second line contains the text "delay=00:00:40". Hmm.

> Dec  2 09:12:05 solar sendmail[21694]: JAA21694:\
>	from=<steve@solar.snyder.net>, size=403, class=0, pri=30403,\
>	nrcpts=1, msgid=<199812021411.JAA21694@solar.snyder.net>,\
>	proto=SMTP, relay=mercury [192.168.0.2]
> Dec  2 09:12:05 solar sendmail[21724]: JAA21694:\
>	 to=<steve@solar.snyder.net>, ctladdr=<steve@solar.snyder.net>\
>	 (500/500), delay=00:00:40, xdelay=00:00:00,
>	mailer=local, stat=Sent

I should also note that I don't use DNS on my LAN. Name resolution is done via a hosts file on each machine.

I haven't done any tweaking of (version 8.8.5) sendmail. It is pretty much as-is from the RedHat installation. In case it isn't already obvious, I'm a newbie at mail configuration issues.

Any advice on how to eliminate this delay in sending mail from my client machines?

Thank you.
*** Steve Snyder ***

Newer versions of 'sendmail' have features that are intended to minimize abuse by spammers and miscreants. Some of these involve doing doubled reverse DNS lookups to check that the forward and reverse names are consistent.

Sendmail normally will not use the /etc/hosts file to map host names to IP addresses. This is because the standards call for it to look up DNS MX records in preference to other types of address records.

In other issues I've described how I get around that on my private LAN (which also doesn't use DNS for mail routing or internal host resolution).

[ Jim has at several points in the past revealed fragments of our main control file, sendmail.cf, so the Linux Gazette search box should be able to reveal it pretty easily if you use that filename as a keyword. -- Heather ]

Copyright © 1999, James T. Dennis
Published in The Linux Gazette Issue 36 January 1999

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