Today I had some free time on my hands, so I tried something that I was planning to do for a long time – properly move away from mbox to Maildir for email storage.
It took me a bit more time than I thought it will, but I have done everything properly with migration of all messages and archives (about 50K emails) and local IMAP server. I have done it on my office workstation, where I am the only user, but the procedure is very scalable and will work fine on any number of users. I am planning to repeat it on the home server which is used by a number of people.