[Dovecot] Overly long email of miscellaneous Dovecot migration questions

[Mark Moseley]

On Wed, Mar 17, 2010 at 12:43 PM, Tony Rutherford <tony at bluetie.com> wrote:
> On 3/16/2010 7:36 PM, Timo Sirainen wrote:
>>
>> On 17.3.2010, at 1.01, Mark Moseley wrote:
>>
>>
>>>
>>> * Since Dovecot 2.0 seems like it's just around the corner, that's all
>>> I've been testing, and indeed all I've even looked at.
>>>
>>
>> Yes, hopefully it's coming soon :)
>>
>>
>>>
>>> * Our #1 main motivation for looking Dovecot is relief for our
>>> currently overtaxed NFS servers, mostly in the form of the index
>>> files. Benchmarking dovecot looks great, even with the index files in
>>> the maildir.
>>>
>>
>> Have you read the thread starting from
>> http://dovecot.org/list/dovecot/2010-January/046106.html and spanning a
>> month or so? That provides a good view of potential problems with NFS.
>>
>>
>>>
>>> * Exim: We currently deliver all of our mail via Exim on separate
>>> servers. Our POP3/IMAP servers only do POP3/IMAP and the Exim mail
>>> servers delivering to maildirs only do Exim. From what I've seen in
>>> the docs and various threads, from what I can gather, the best thing
>>> to do in that case would be to use Exim's built-in maildir handling,
>>> instead of using 'deliver'. That would be my preference anyway, but I
>>> wanted to make sure I didn't misinterpret things.
>>>
>>
>> v2.0 supports also LMTP server, so you could deliver to Dovecot that way.
>>
>>
>>>
>>> * Any problems running Courier POP3 and Dovecot IMAP for a while,
>>> possibly Courier IMAP and Dovecot IMAP concurrently?
>>>
>>
>> Courier POP + Dovecot IMAP is fine. But concurrently running both POPs or
>> both IMAPs is just going to cause trouble because of conflicting UIDs. You
>> might be able to make both Dovecot and Courier use the same POP3 UIDLs, but
>> I wouldn't really trust it.
>>
>> One possibility would be to just run the migration script on login, so
>> users would migrate to Dovecot as they log in.
>>
>>
>
> I would add a big warning as well to running Courier and Dovecot
> concurrently.  If users are strictly segregated to using one or the other
> (consistently), then strictly running Courier and Dovecot on the same
> machine is not an issue (on different ports or whatever).  But, I would NOT
> recommend having it such that a user could hit Courier one time and Dovecot
> another...I think that is begging for big trouble.  As Timo mentions, most
> of the trouble will be with syncing the UIDs.  Even running POP Courier and
> Dovecot IMAP might be a problem...especially if your users can use both POP
> and IMAP....Courier has 2 uidl files,  (at least the version we were
> migrating from)..one for POP and the other for IMAP, and they get combined
> to one in Dovecot (dovecot-uidlist).  Then if a user comes in via
> Dovecot...and updates the dovecot-uidlist...by definition the Courier files
> would be out of date.  I would really steer away from that approach.

I'll definitely keep that in mind. I should be able to keep things
pretty segregated in terms of POP3 alone or IMAP alone but my big
worry is that Courier POP3+Dovecot IMAP scenario. I'm thinking
especially of people using POP3 in one place and webmail in another
location. I'm guessing that people using POP3 in one location but
direct IMAP in another are fairly rare. Whatever the case,  it sounds
like I need to do some log analysis to see what % of people access in
both ways. Thanks for the advice!