Makes sense but that's what I did and still got the error. Even though Opera Mail (and Opera) was closed at the time maybe I copied the files while omailbase.dat was in an indeterminate state. Thanks for the feedback though!

leocg has the right idea. If I copied the mail folder to a new location and started Opera Mail I received the following error:

Error While Initializing Mail

There was a problem initializing Opera Mail.

Failed to open the following file:
=D:\hold\Opera\mail\omailbase.dat

..BUT if I do

• a fresh install of opera mail
• copy the mail folder to new location
• start Opera Mail and setup accounts

THEN it works!

Notes:

• Tried reboot before starting Opera Mail after copying folder and setting Mail Root Directory but it still gets error
• Changing the install path during install changes the program folder but not the data folder
• Be sure to do a fresh install and change Mail Root Directory before setting up email

Thanks leocg!
Karl

I see that Opera Mail is storing mail in C:\Users\XXX\AppData\Local\Opera Mail\Opera Mail\mail but is there any way to change that or parent folder location? I believe setting "Mail Root Directory" in one of the opera.ini files pre M2 / Mail breakout did this before but I don't see any settings like that in operaprefs.ini or accounts.ini ..any ideas?