On 1/4/2011 9:38 AM, Jeff wrote:
Here are our relevant specs.
sendmail-8.12.11-4.RHEL3.6 (we may not be able to upgrade this due to too many modifications) imap-2002d-14 procmail-3.22-10.el3.centos.0
Regardless of the maildir vs mbox argument, I would be seriously examining why you have painted yourself into a corner with your customized sendmail. Eventually, you will have to move on.
Errr, why??? Sendmail has nothing to do with local deliveries.
What are the motivations for the customizations? Do newer or alternate MTAs have added features that can replace those customizations? Postfix can be highly customized through configuration and is not that difficult to learn.
Why change the part that isn't broken.
As a migration path, I would separate the MTA (sendmail) and the imap server. Go with cyrus or dovecot on a new machine (virtual?) and use imapsync to move messages to the new box during a maintenance window. As stated in other responses, cyrus has it's own mail storage format with individual files for each message and dovecot supports several formats including maildir. It should not be difficult to have your existing sendmail deliver messages to the new imap store either directly or with a very simple postfix MTA on the imap box. Once mail storage is fixed, you can start working on de-customizing your MTA.
Sendmail will let cyrus or procmail or another local delivery agent handle the file format details - and probably already does.
And with regard to backup space, it might be time to suck it up and tell your users that you need to implement mail quotas. How much are you backing up from "Sent" and "Trash" because nobody maintains their mail folders? A quota can be a great tool for teaching basic mail folder housekeeping.
Anything that does sensible incrementals will use much less space with 'file-per-message' formats instead of mbox because the bulk of the messages won't change between runs. But maybe another solution would be to put the backups on a block de-duplicating filesystem like zfs.