Migrating from Virtualmin 2.50(gpl) to 3.35(pro)

Alright, so I’m trying to migrate servers from an old box to a new one. Best way I can think of is to backup all my 2.50 domains via the backup command then ftp them over to the new box and restore them. All 138 of them, blah.

Problem is that the old system uses Sendmail and its mail system, so I don’t get any of the mail that was backed up. I was thinking about fetch-mail but then realized that I had over a thousand users I would have to do that for.

Good news is that all the users will have the same usernames, and same username structure.

My question, is there a way I can migrate mail with the domains?
If so, what would be involved?