Solved a little bug hopefully

[BosieIonut]

When you are trying to connect to a domain with the dot at the end (ex: mta5.am0.yahoodns.net. instead of mta5.am0.yahoodns.net) the smtp connection works just fine but starttls() will raise an handshake execption.

[ghost]

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[bitdancer]

I would like to understand why this produces an error. A domain name with a trailing '.' has a meaning: don't try to resolve this name with a local extension (see /etc/resolve.conf 'search' control). So passing the trailing dot through is the correct behavior, and I'd like to know why starttls is failing. Is this a bug in (some implementations of?) starttls? An RFC disagreement (I hope not)?

[skirpichev]

Thanks for your contribution, but it's no-go as is.

This worth an issue (please open) and a changelog entry. Also, please do pr wrt the main branch, not against the maintenance branch. See also https://devguide.python.org/