I recently added old Yahoo e-mail account to Thunderbird version 60.5.0 to access a Yahoo groups list. But kept getting error message that I could not connect to imap.mail.yahoo.com. I researched a bunch of answers, thinking perhaps it was Malware Bytes goofing everything up. But added suggestions to MBytes 'ignore' list and still error. And then I noticed in Thunderbird recommended port # of 993. I had gone thru the 'automated' setup for IMAP (not POP) and was pretty sure TBird chose port 995. As soon as I changed to port 993, wow...the e-mail messages flowed in! Problem solved. So, this might be an issue for some folks -- so in TBird, View Settings for Account, click on Server settings and at the top of the window, check that the port number should be 993 and not 995.