Unable to send mails with smtps://smtp-relay.gmail.com:465

[vizv]

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• I could not find a solution in the existing issues, docs, nor discussions.
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Describe the bug

Unable to send mails with smtps://smtp-relay.gmail.com:465

See below for relevant configuration, context, and workaround

also attach this ticket to #781

Reproducing the bug

Configure courier.smtp.connection_uri to smtps://<g-suite email address>:<application token>@smtp-relay.gmail.com:465/ and send any email (verification / recover / ...)

Relevant log output

No output but netstat shows the courier is continuously attempting to send the mail out.

However when setting RetryFailure: false for gomail.Dialer in courier/smtp.go, I'm able to get error like:

func=github.com/ory/kratos/courier.(*courier).dispatchEmail
file=/go/src/github.com/ory/kratos/courier/smtp.go:184
error=map[message:gomail: could not send email 1: EOF stack_trace:stack trace could not be recovered from error type *mail.SendError]

Relevant configuration

courier:
  smtp:
    connection_uri: smtps://fake@domain.tld:fake-token@smtp-relay.gmail.com:465/

Version

v0.9.0-alpha.3

On which operating system are you observing this issue?

Linux

In which environment are you deploying?

Kubernetes with Helm

Additional Context

After hacking around, I found the issue is caused by ory/mail module trying to handshake with gmail relay server with EHLO localhost since LocalName of the smtp dailer is not set (and localhost is the default local name) but gmail doesn't like it:

if I use openssl to establish an SSL connection with the server and send EHLO localhost, it will return 421 and hang up immediately:

openssl s_client -crlf -connect smtp-relay.gmail.com:465
...
220 smtp-relay.gmail.com ESMTP v9-... - gsmtp
EHLO localhost
421 4.7.0 Try again later, closing connection. (EHLO) v9-... - gsmtp
read:errno=0

similar to https://stackoverflow.com/questions/65721463/phpmailer-not-sending-emails-from-localhost-using-gmails-smtp

However the current implementation doesn't support setting LocalName from config, in fact I tried to hard-code LocalName to "kratos" and it just works.

Another minor issue is RetryFailure: true makes back-off strategy not working as expected, for smtps://smtp-relay.gmail.com:465 it's continuously re-establishing connection silently and never stops or back-off exponentially.