[Dovecot] Courier migration and vpopmail with dovecot-lda

[Charles Sprickman]

I've been using Dovecot in some fresh installs lately and have found
it fairly easy to configure.  However I'm starting on a migration
that involves moving from some very old software (ancient vpopmail,
qmail and Courier).

On the Courier front, I've reviewed the migration page in the wiki,
and it looks like the main concerns are just matching the namespace
and then using the migration script to create new subscription and
uidlist files.  Given that my Courier IMAP setup is so old (4.0.6),
is there anything to be aware of that's not covered in the wiki due
to the age of Courier here?

Are there any other general issues to be aware of as far as
interactions with MUAs are concerned?  For example, if Courier has
been presenting the user's MUA with a given set of IMAP capabilities
and then the MUA sees a bunch of extra capabilities on a subsequent
login, will that trigger any strange behavior?

And lastly on this subject, I will obviously be doing some testing
before cutting over to the other server.  Is it valid in something
like Thunderbird to have it pointed to "imap.domain.com" and then
change the imap server to point to something like
"testimap.domain.com" for testing whether subscriptions and the
uidlists are working as expected or should I fully replicate the
move as an end user would see it by making the change in my local
hosts file?

Now, assuming that portion of the move goes alright, I'm incredibly
confused about getting Dovecot and Vpopmail working together.  I
assume that initially I can stick with the Maildir++ mailbox format
and let vpopmail's vdelivermail continue working as my LDA -
vdelivermail understands how to find the user's Maildir, it can
check quotas, and it can update the maildirsize file (which I'm
assuming dovecot can also read and then report quota/usage to an
IMAP client).  However it does look like the Dovecot-only mailbox
format(s) will offer much better performance than Maildir as the two
dbox formats are the only supported mailbox formats with separate
index files, correct?  Is there any guidance on how to use dovecot's
LDA with a virtual mail system such as vpopmail?  From what I've
read so far, I probably don't want to use the vpopmail extension
supplied with dovecot, but query the mysql vpopmail db directly.
I'm finding a ton of info while searching for this, but most deals
with older versions of dovecot, and there are also many "this works
but I don't know why" tutorials on combining dovecot and vpopmail
and dovecot's own LDA.  I'm not even able to guess how one handles
the per-user .qmail files in vpopmail if not using vdelivermail
(this is where we enable/disable spam filtering by piping the
message through spamc).

Any input on the overall migration process is appreciated.  It's a
bit overwhelming as I have to deal with a big jump in the vpopmail
version, rebuilding qmail with a ridiculous number of patches, and
then on top of that a migration to new imap/pop server software.
eek.

Thanks,

Charles
-- 
Charles Sprickman
NetEng/SysAdmin
Bway.net - New York's Best Internet www.bway.net
spork at bway.net - 212.982.9800