I have to ask: If you are using WLM 2012 strictly as a POP or IMAP access e-mail client why would you have to change?
There are no indicators that WLM 2012 has become a security risk and the POP and IMAP protocols have been virtually untouched for decades now. Until something comes out indicating that a new exploit (or exploits) are targeting WLM 2012 successfully it's probably as secure as most of the currently available e-mail clients. Official support only stopped in January.
If you are using IMAP access you don't need to save anything (unless you moved it to a strictly local folder) as IMAP folders are on the mail server and will be re-created when you enter your account information in an alternate e-mail client if you wish to use one.
My first choice is Thunderbird. Opera Mail is quite nice, too.
Brian AKA Bri the Tech Guy (my website address is in my profile) Windows 10 Home, 64-bit, Version 1709, Build 16299
Here is a test to find out whether your mission in life is complete. If you’re alive, it isn’t.
~ Lauren Bacall