Subject: Desperate : ipop timeouts

From: Tom Combs <[email-masked]>
Date: Thu, 16 Dec 2004 11:52:32 -0500 (EST)

Hi,

  I have Eudora and Outlook clients that get frequent to occasional 
  connection time outs when checking mail. I believe this is exclusively
  for the pop users but may be for imap also. We have ~300 users and
  the ratio of pop to imap is about 15 to 1.
  
  The problem we are seeing is that a check for incoming email will
  occasionally cause a timeout error: 
    
   Could not connect to "mail.magnet.fsu.edu"

   Cause: Connection timed out (10060)
 
  Other attempts will be successful, with some timing out. Some users
  get this a lot, some only a few an hour. I see no relationship to the
  size of the incoming mailbox and the error.
 
 The server load level is low, usually 0.5 to 1.0 and top shows it
 hardly breaking a sweat. I see no errors in the log files to indicate
 what the problem is.
 
 The server is a dual processor Dell Power Edge 1750 with 2GB of RAM.
 It is running RHEL 3.0, sendmail 8.13.1 and UW IMAP 2004a.
 
 I've played with sittings for xinetd by increasing the number of connections
 allowed, turning off LIBWRAP and other things but nothing helps. I've also
 tried increasing the buffer size in the Advanced Network settings for Eudora 
 but this doesn't help either. 
 
 Do realize that this is an intermittent problem for individual clients. They
 will get the timeout but then they can turn around and check their email.
 
 I was running may email services under Solaris on an Ultra 10 which is
 not nearly as powerful as the dual Xeon PowerEdge 1750 and never had
 this problem with the same load.
 
 I have done a lot of searching and have not see anyone with this problem.
 I hope you guys have seen this before and can save my holidays!

 Thanks!     --Tom Combs

--
Tom Combs                                      E-mail: [email-masked]
National High Magnetic Field Laboratory        Phone:  (850) 644-1657
1800 E. Paul Dirac Drive                       Tallahassee, FL 32310

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From: Mark Crispin <[email-masked]>
Date: Thu, 16 Dec 2004 09:06:31 -0800 (PST)

The connection timeouts that you are getting have nothing to do with 
ipop3d; they indicate that ipop3d has not even started!  So, you were on 
the right track with increasing the number of connections allows in 
xinetd.

Unfortunately, problems such as these require more investigation before 
any definite solution can be found.  The first thing to determine is what 
your POP users "new mail check interval" is.  Unlike IMAP, POP requires a 
new connection for each check of new mail.  So, if the user is checking 
for new mail every second, a new POP session is opened every second!

Opening a POP session is expensive; SSL/TLS encryption needs to be 
negotiated, login authentication needs to be negotiated, and the mailbox 
has to be processed.  On top of that, [x]inetd limits the number of POP 
sessions that can be spawned each minute.

So, take a look at the mail syslog and see if you can find any obvious 
users who are abusively checking for new mail at an excessive rate.  Quite 
frankly, people who need faster than once/minute checking are badly in 
need of a life; and I personally advocate once every 3 minutes.

Your server should be more than capable of the user load.  I think that 
you are running up against [x]inetd.

Also -- gently -- suggest to your users that they really should be using 
IMAP instead of POP.  IMAP notifies of new mail within the session, so it 
isn't necessary with a good client (such as Pine) to re-open new sessions 
all the time.

I can't speak intelligently about what either Outlook or Eudora may do 
with IMAP; it sufficies for me to know that Pine is better. :-)

-- Mark --

http://staff.washington.edu/mrc
Science does not emerge from voting, party politics, or public debate.
Si vis pacem, para bellum.