I recently found em client and decided to give it a try for my business email. I really do not like te Win 10 Mail app. Thunderbird’'s design is horrendous.
Anyway, when I enter the details as instructed by my mail server, em client works if I choose Non-Secure SSL ports. However I want to use Secure SSL. Using ports 993 and 465 for IMAP and SMTP respectively doesn’t work. em is unable to connect to the server to fetch the email.
To use SMTP SSL you have to choose the correct Security Policy that matches your ISP SMTP IMAP server settings. They are not all the same.
I use Gmail which works for me on SSL - “Force usage of SSL/TLS” with Port 587 . If you cannot get any of the SSL security policy options to works with Port 587 then contact your ISP and advise.