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Re: Building an IMAP server

On Sat, Feb 01, 2003 at 02:08:18PM +0100, Hans Wilmer wrote:

> Currently I'm trying to figure out what software to use best to set up
> an IMAP server for the company I'm working at. I'll be using Debian
> Woody for the server, and the following requirements and suppositions
> are given:

... well, commenting myselfe :)

Thank you very much for your nice feedback so far!

It seems that the imap part of courier fits nicely into what I
want. I've done some testing by installing it on my server here at
home to access the ~/Maildir of a testuser, using squirrelmail, imp
and the mozilla client. To have a few mails to run the tests on, I
copied over my debian-users maildir folder that currently holds 37638
mails. Also, I've been using rsync, as suggested for making backups,
to keep the copy of the folder in sync, and it works very well :)

But there are some issues/questions that came up:

1.) performance:

    My server has an IDE disk only, and it turned out that imapd
    tends to heavily access the disk. Performance (700 MHz Athlon)
    is ok for one user, accessing a folder holding a handful of
    mails only. But when accessing the debian-users folder, it takes
    quite a while until mails are displayed, and access is unusably
    slow when sorting the mails by date. When trying to get a threaded
    view with squirrelmail, the PHP script even times out.

    Performance depends on the client used. The mozilla client works
    fine even when creating heavy load on the server by accessing the
    same debian-users folder with several clients. The webmail clients
    time out.

    When there's load on the server, even apache can get to eat up
    almost 100% CPU. This results in not responding to other requests,
    what seems not exactly acceptable. It can't be that one user
    blocks the server so that others can't do anything but wait. Users
    would loudly complain.

    How can I get the best performance and prevent the server from
    being blocked by single users (letting aside using good disks and
    maybe RAID)? Using large amounts of RAM doesn't seem to help.

2.) local users:

    As mentioned in my other mail, users will not have a shell login
    to the server. They'll access it solely with the IMAP clients.

    What security issues are against creating local users under these

3.) filesystem:

    One of you suggested to use xfs. It has the advantage of, at least
    theoretically, making better use of the disk space and wouldn't
    have inode limitations. It claims to be faster in maintaining huge
    amounts of relatively small files, as would be the case with using

    But once I tried it xfs on my workstation, and I managed to
    destroy some data by remounting partitions from read only to rw
    and vice versa. I was lucky as the partitions that were damaged
    only contained some games I could reinstall from the CDs, but the
    experience lead me to remove xfs and get back to ext2 (and now
    ext3). That I destroyed data on the xfs partitions was very
    probably due to my own fault by not specifying the correct
    parameters when doing the remounts. I couldn't verify that because
    I removed xfs before I noticed that it might have been my fault.
    However, my conclusion was not to use xfs unless it's really
    neccessary for the ACLs it provides. May it be stable or not, ext3
    seems much easier in handling than xfs, thus making it less prone
    to mistaken handling.

    Is using xfs instead of ext3 actually such a big advantage (in
    speed) that this justifies the more complicated handling?

    Where do I find more information about the mount options of ext3,
    as mentioned in

4.) quotas:

    What will happen when a user reaches the quota limit so that exim
    cannot deliver any more mail to his ~/Maildir?

    In your experience, how much disk space will users actually need
    to store their mails?

5.) hardware:

    Any special hardware recommendations? Maybe a dual processor
    maschine? Hm, won't make much sense with IDE disks ...


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