Migration Strategies?

[Andrew Morgan]

On Fri, 30 Jan 2004, Andrew J Caird wrote:

> Hello all,
>   I'm starting to think about migrating away from UW-IMAP (for the reasons
> mentioned a few days ago on this list) to a Cyrus IMAP server that we've
> been using for some people for a while.
>   It's easy enough to migrate everything except the inbox with mailutil,
> and in my (so far) limited testing that works pretty well (see below).
> However, how do people deal with migrating the inbox, given that it can
> change during the migration?
>   More specifically, the email gateway is currently configured to deliver
> email to, for example, acaird at uwimap.fccc.edu.  I migrate that inbox, and
> before I can switch delivery to acaird at cyrus.fccc.edu, more email comes to
> acaird at uwimap.fccc.edu.  Then what?  Alternatively, if I start delivering
> email to acaird at cyrus.fccc.edu and then migrate on top of it, does that
> cause any problems?  It seems like the second choice is the best one, but
> some confirmation from someone who has done or understands this would be
> much appreciated.
> --
> Andrew Caird            andrew.caird at fccc.edu               215.728.4071
> Email Administrator                              Fox Chase Cancer Center

Or just defer delivery until after the migration, then switch all the
names at once.  For our migration, we changed the MX for our site to point
to our campus mail relays and let the mail pile up there until the
migration was done.

One thing to watch out for is the default "delayed delivery" bounce
notices are sent out by most mail servers after 4 hours.  So if you plan
to be down longer than that, people sending mail to your users may get one
of these bounce messages.  If you are using an internal mail relay to
queue up mail during the migration, you should increase the timeout from 4
hours to however long you plan to be down.

	Andy