I’ve had a similar issue with the Microsoft Outlook servers Unable to send email using office365 smtp servers · Issue #114 · gen-smtp/gen_smtp · GitHub The Outlook servers close the connection as soon as an SSL request is sent before a subsequent TLS request. However, the Google Email servers didn’t seem to have this problem. The problem with erlang ssl is that during the tls connection setup it first (incorrectly) sends an SSL request and then tries to send a TLS request. The fix for this is to always pass [{:versions, [:'tlsv1.2']}] as an option while doing ssl connections.
