[TriLUG] Imap software preferences

[Jeremy Katz]

On Mon, 2002-08-05 at 00:30, John Franklin wrote:
> On Sun, Aug 04, 2002 at 10:31:18PM -0400, Tanner Lovelace wrote:
> > that's about it.  Does anyone have any preference for imap server?
> > Speak now and forever hold your peace. :-)
> 
> If memory serves me right, the Cyrus server may be faster, but it puts
> all the mail in a database that's understood by only Cyrus.  Which means
> that even on the IMAP server we have to use IMAP to get mail.

Yes.  And it's loads faster.  And more scalable.  The administration,
from what I gather from our IS guys, is a breeze as well.  The downsides
to Cyrus according to everyone I've ever talked about mail stuff is: can
only access the mail via imap (not necessarily a horrible thing, though)
and the setup is a little bit more complicated.
 
> Maildir format is understood directly by a handful of mail clients. It
> keeps every message in a separate file.  Does the standard subdivide the
> mail folder?  That is, does it limit a directory to, say, 500 messages
> then start a new sub-folder?  Large directories put strain on ext2/3 and
> other UFS derived file systems.  The directories are kept as an unsorted
> linear list.  In order to do a create, the entire list must be traversed
> to insure the filename doesn't already exist.  It also means that every
> message will take up at minimum 1 fragment (typically 1k or 4k.)

Yes, maildir will get a little bit slow if you have mailboxes with on
the order of multiple thousands of messages.  Then again, I had
mailboxes at work with 15000 messages and didn't really feel any pain
from it (other than refreshing 15000 headers over a cable modem is slow
no matter how you cut it :).  Courier is a fairly nice IMAP server, easy
to set up and you can safely let clients access the mail directly via
NFS if you go this route.  

> Mailbox format, as supported by the vast majority of mail clients and UW
> IMAP, is a single file per user.  Large mailboxes can take time to scan.
> I think UW mmap()s the mailbox, which means they don't get swapped to
> the swap partition.  In case anyone cares, UW IMAP also comes with a
> pop server.

UW is a security nitemare and horrible in the performance area.  Having
two or three people using big mailboxes via UW off of a server will
definitely have a noticeable impact.  Also, if you go this route, you do
*not* want to let people access their mail spools directly via NFS. 
There's no real locking involved so mail can and will get lost.  

> Any of them can be SSL'd though sslwrap.

Actually, all of them have built-in SSL support these days, so that's
not really a concern.  
 
It really depends on how much you think the resource is going to be
utilized and how well you want it to scale.  Cyrus is a little bit more
initial investment to set up (but it really wasn't too bad from what I
remember) but is probably the best bet if you want a real long-term
solution.  Either of courier or uw are reasonable low to mid-range
servers, although I really have not been happy in my past experiences
with uw-imap

Cheers,

Jeremy