I've asked for help on this on the Apple board:
as well as some other venues but so far no one has come up with an answer.

I thought I'd try here as I just found this board.

re: Intel iMac circa 2009 with Time Cap and current Mav.

This has been happening since Mt Lion.

When I use Time Machine (via my Time Cap) with Apple email, when I'm done and TM is closed, the Apple email's Accounts.plist has been overwritten. No matter if I restore an email or not, the plist gets written (set back) to an earlier version.

Even if I don't restore an email or even go back in time, simply entering Apple Mail Time Machine causes a new Accounts.plist to be pulled from somewhere and written in place of the current one.

I know this because the plist has old return-email and other data in it. Of course, this screws up my Email big-time.

I've looked all over (via PathFinder search of system files) and I can't find out another copy of the plist or its data anywhere on the hard drive. My only guess is that the data in the plist is cached somewhere in TM on the TC? I'm rather technical, being a programmer for many years... but this one has me stumped.

Does anyone have a clue as to what is happening? Maybe give me an idea where else to look for where this old data is coming from? I need a fresh sent of 'eyes' and brains on this... someone who can think more outside the box than I have!

(Note: before going to TM I now always make a copy of the plist so I can restore it once leaving TM.)

Thank you.