How can I debug a 'connection refused' problem?

[Frank Thommen]

Dear postfix-users,

we have a weird problem with one of our several mailservers: From time
to time it gets into a state, that it refuses to receive SMTP
connections from our mailrelay in _most_ (95%), but not all cases
("connect to <remote_server>[<ip>]: Connection refused").

At the same time it is possible to telnet to port 25 of the refusing
server and send mails without any problem. Until three days ago it
helped to restart sendmail on the remote server and to requeue the
appropriate mails on the central relay. But currently mails are
accumulating ...:-(


The mailrelay is running postfix 2.0.16 (Solaris 9), the remote server
is running sendmail 8.9.3 (Solaris 2.6.1). The identical setup works
fine for all other mailservers we have (updating is currently not an
option).


I tried debugging by setting the following in main.cf:

debug_peer_level = 9
debug_peer_list = <remote_server_name> \
<fully_qualified_remote_server_name> \
<remote_server_ip>
error_notice_recipient = <my_full_email_address>
notify_classes = resource, software,protocol

Nevertheless I don't get any useful information nor in the maillog nor
in any error mails.

What other possibility do I have to debug this problem? Tell me if you
need more info.


Thanks in advance

frank

----------
Frank Thommen, Informatik Support Gruppe, D-INFK, ETH Zuerich
E-Mail: ***@inf.ethz.ch; Tel: [phone] (Mo-Do)
Web: http://www.isg.inf.ethz.ch
----------

[V***@morganstanley.com]

Post by Frank Thommen
we have a weird problem with one of our several mailservers: From time
to time it gets into a state, that it refuses to receive SMTP
connections from our mailrelay in _most_ (95%), but not all cases
("connect to <remote_server>[<ip>]: Connection refused").
At the same time it is possible to telnet to port 25 of the refusing
server and send mails without any problem. Until three days ago it
helped to restart sendmail on the remote server and to requeue the
appropriate mails on the central relay. But currently mails are
accumulating ...:-(
The mailrelay is running postfix 2.0.16 (Solaris 9), the remote server
is running sendmail 8.9.3 (Solaris 2.6.1). The identical setup works
fine for all other mailservers we have (updating is currently not an
option).

Don't blame the messenger. Fix Sendmail (the one refusing connections) not
Postfix. This is not the best forum for Sendmail advice, but FWIW consider
removing or raising the "RefuseLA" setting in sendmail.cf.

[Frank Thommen]

Post by V***@morganstanley.com

Post by Frank Thommen
we have a weird problem with one of our several mailservers: From time
to time it gets into a state, that it refuses to receive SMTP
connections from our mailrelay in _most_ (95%), but not all cases
("connect to <remote_server>[<ip>]: Connection refused").
At the same time it is possible to telnet to port 25 of the refusing
server and send mails without any problem. Until three days ago it
helped to restart sendmail on the remote server and to requeue the
appropriate mails on the central relay. But currently mails are
accumulating ...:-(
The mailrelay is running postfix 2.0.16 (Solaris 9), the remote server
is running sendmail 8.9.3 (Solaris 2.6.1). The identical setup works
fine for all other mailservers we have (updating is currently not an
option).

Don't blame the messenger. Fix Sendmail (the one refusing connections) not
Postfix. This is not the best forum for Sendmail advice, but FWIW consider
removing or raising the "RefuseLA" setting in sendmail.cf.

Hmm. I'm not looking for sendmail advice. What I need is advice how
to get a detailed SMTP session transcript on the Postfix side. The
host can receive mail from other hosts w/o problems, but not from the
Postfix relay. Therefore I want to look there for the problem.


Regards

frank

[Len Conrad]

Hmm. I'm not looking for sendmail advice. What I need is advice how to
get a detailed SMTP session transcript on the Postfix side.

master.cf, add -v to smtp line, send to sendmail, then remove the -v

or of any very busy postfix, use the debug peer feature to debug only with
the IP of sendmail.

Len


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[V***@morganstanley.com]

Post by Len Conrad

Hmm. I'm not looking for sendmail advice. What I need is advice how to
get a detailed SMTP session transcript on the Postfix side.

master.cf, add -v to smtp line, send to sendmail, then remove the -v
or of any very busy postfix, use the debug peer feature to debug only with
the IP of sendmail.

With connection refused there is nothing to debug. The remote host is not
listening and Postfix backs off, unlike other MTAs Postfix remembers that
the host was dead and backs off for a while.

As I said, fix sendmail by disabling RefuseLA!!! See the recently posted
QSHAPE_README file in the archives for an ugly hack for transmission into
a noisy channel, but better yet, fix the Sendmail host!!!