I'm trying to set up exim4 on my Debian/Buster server to work with my new ISP (Rogers.com). They require an SSL connection on port 465, which isn't unusual, but I can't get it to work. They do require something they call an app password for unusual programs, which seems to be just a very strong password that they generate for the account.
I've set passwd.client to use all the various servers that seem to be connected with smtp.broadband.rogers.com as it sends e-mail (e.g. *.yahoo.com, *.yahoodns.net) so that it should use the app password no matter where it's asked for it.
I've also used the advice from https://halon.io/blog/how-to-test-smtp-servers-using-the-command-line/ to test my connection. In particular, after trying the command
openssl s_client -connect smtp.broadband.rogers.com:465 -starttls smtp
and the same thing without the -starttls smtp, I concluded that it isn't requiring starttls. This is confirmed by my Thunderbird settings.
I was able to log onto the smtp server using the base64 encoded username and app password (as per halon.io's instructions) for the account I'm trying to send mail from.
Of course rogers doesn't support Linux so I need help to find out how to make this work.
I believe that Debian compiles exim4 against GnuTLS rather than the OpenSSL package I used for my tests, but Debian's wiki suggests this shouldn't be the issue.