For what it's worth, I have been having some luck with an old email friend from XP called Outlook Express. I see no need for a large email client, like Outlook and I have seen similar "new" programs like Classic OE and even have downloaded and installed the free version. It's problem was associating itself with my Outlook Express Databases in a separate G: drive I have on my computer. I set up all the store folder in my XP Partition in one folder, with each email account in it's own folder.
Now with a new Outlook Express program I got from
http://www.RunAsXP.com it has been going fairly well getting a syncronization between the 2 different operating systems and the share of several email addresses stored in separate folder (under one folder) on one of my drives. Since they each use the same .dbx format, as it really is Outlook Express 6 but tweaked to actually work within Windows 8.1. Classic OE used a similar but different database called an .mbx
Now when I open my email in OE in widows 8.1 I can see all the previous emails in the inbox, as well as in each individual folder and custom folder I created in my XP. On top of that any new email is stored in the same "named" folder in that folder of databases. So, when I go back into XP I can open OE and low and behold all the emails I sent or downloaded when in Windows 8.1 are all there as well.
Just passing this along... Even though the OE that is at the runasxp site is in essence, Outlook Express by Microsoft, it is really not sold by them. You have to donate a minimum of 10.00 to become a member, and then you can download as it is only open to members. This way I guess it gets around the "can't sell" portion of the license agreement, as you are just donating to become a member of the forum and the download is only available for supportive members.
This link shows a little bit of the program.
http://runasxp.com/Thread-Outlook-Expre ... 0-DOWNLOADI, for one am glad for it as that was one determining factor (lack of a decent start menu was the other) for not getting more involved in other newer stuff from MS as I liked, and still DO, Windows XP.