I, too, am looking at the feasibility of migrating from 2.72 to 4.2.2. To be on the safe side, I was thinking of copying my entire existing 2.72 setup to a spare computer and running a test install of 4.2.2 on top of it. If that works, then I would install 4.2.2 on my production setup.
Does that sound to you like it would work?
BTW, one reason I'm looking at migrating is that the webmail client on my 2.72 setup sometimes won't load JPGs inline: it just displays a small box with a torn page in it. I've tried modifying the images a bunch of different ways but nothing has helped. It's not all images, just some. In any case, I just installed the free version of 4.2.2. to test and the client loaded the current problematic image just fine.
A main reason I love AMS is that it does
NOT require a relational database. I much prefer a flat file system because I can relocate it to another computer with an absolute minimum of effort and risk. My email server data is very low, so I don't need the speed of an RDMS.
Finally, one feature I've always wanted in AMS (and the main reason I haven't upgraded yet) is for a single query to be able to search through multiple folders, and subfolders. Does 4.2.2 have this (Ikon crosses his fingers and prays really, really hard
)
Sorry to get OT a bit, but I couldn't see much point to creating multiple posts.