Network failure / socket closed error after upgrading to OTP26

[zambal]

Describe the bug

We use gen_smtp for sending emails, currently using postmark SMTP servers. After upgrading to OTP26.0.2, sending e-mails fails with this error:

send email error: :retries_exceeded {:network_failure, ~c"52.208.184.61", {:error, :closed}}

These options are used:

[ relay: "smtp.postmarkapp.com" username: "...", password: "...", port: 587, ]

Platform

OTP: 26.0.2
Elixir: 1.15.2

[seriyps]

It's not enough information to suggest anything. Can you at least try to enable "tracing" and add here the output?

In Erlang you do it by providing trace_fun option:

gen_smtp_client:send(Email, [{trace_fun, fun io:format/2}, {relay, ...}])

[mworrell]

If it is since OTP 26 then I suspect a duplicate of #328

[zambal]

Sorry for the short description and lacking information, I was a bit in a hurry.

I just tried sending an email with the trace option enabled and although the resulting error tuple is different, it turned out to be the same issue as #328 indeed.

After setting

[{tls_options, [{verify, verify_none}]}]

or

  Opts = [
    {verify, verify_peer},
    {cacerts, certifi:cacerts()},
    {depth, 99},
    {server_name_indication, "smtp.postmarkapp.com"}
  ]
  [{tls_options, Opts}]

all works well again.