Do you have a backup of eM Client ?
If you have had enabled periodic backups, or done a manual backup with EMC, go to “Menu / File / Restore” and you can restore previous backups.
If you have done a backup with an earlier version of eM Client and won’t restore, you can obtain that via the following webpage - https://www.emclient.com/release-history
Also see the following EMC Thread on AOL/Verizon with regard to account protocols and port settings that might help you.
AOL/Verizon just changed there POP and SMTP setting and now EM Client will not work. - eM Client