Email Hostname Certificate Mismatch Causing sidekiq Queue Overload, Severe Site Instability

Bump, @pfaffman and/or @codinghorror.

Do you think we may have a bug here, or something else?

1 Like

@gunnar I moved your post here since this is the email issue you’re describing.
I am not sure if the “post has already been taken” error is also being caused by this, but the details you gave about your email belong to this issue.


It seems absurd to me that after 30 days there is still this problem…
I had to change my email provider to get my forum working again.

1 Like

That is frustrating, but it looks to me like some gem no longer supports ignoring b invalid certs and/or unencrypted transport. It may just be the case that the days of being able to send mail that way are over. But I’m not experiencing the problem myself, so I haven’t looked carefully enough to know if I’m right.


Is there a way to “downgrade” discourse to an older working version (say 2.8.0 stable or 2.9.0 beta3) until this is worked out?

1 Like

I decided to spend one more half hour to dig into this and I think I found the cause.

This seems to be related to the move to Rails 7, which updated net-smtp from 0.1.0 to 0.3.1, which changed the defaults.

The way the smtp gem calls net-smtp does not disable enable_starttls_auto and openssl_verify_mode, it only enables it when enabled.

Related: SMTP: allow disabling starttls_auto since it's now true by default in Ruby 3 by jeremy · Pull Request #1435 · mikel/mail · GitHub


Nice work, Richard! That would have taken me two hours if not twice that. For me it’s easier to succumb to dealing with the new defaults.

Aha. So I was sort of right, it’s just that it might not be too hard for a PR to fix it.


Nice job @RGJ!

While we anticipate a fix, on a side note, it would be good if this problem didn’t cause the cascade of issues that I experienced, which nearly brought by forum down completely. Specifically:

  • The email failures seem to be retried extremely quickly, which causes the sidekiq queue to explode in size and ~100% CPU usage caused by these tasks
  • In addition, something (either crashes or restarts) was causing Redis to write enormous tmp files, I assume containing the state of the sidekiq queue. While these were safe to remove, they quickly filled the disk, which cause more crashes, and so on. I had some other disk space that I was able to free so that I could restart the forum and figure out what was going on, but this may not be true for everyone. (It’s also somewhat hard to confirm that, in this case, the Redis tmp files are in fact safe to delete.)

My guess is that the simplest solution here is to slow down the retry on failed email jobs—or at least on ones that don’t have timeliness constraints like password resets. Which seems appropriate given that email problems are unlikely to resolve quickly, and most / all mailers will do their own retries once they receive a message.


In my case when I encountered the failure after the upgrade it was using TLS with a third party server and the name on the certificate matched the smtp server name. I just had one failure however. I haven’t rebooted or upgraded since to avoid further issues. I’ll try an update once the patch has been released and see how it goes.


I’ll start by creating a topic in #bug but since it’s technically a problem in an upstream gem I am not sure how much priority this is going to get.


+1 :worried:really frustrating bug

1 Like

Can’t the gem be rolled back? I would be surprised if it didn’t get attention since this is a “core” functionality, the ability to send emails and for some it’s also causing an outage due to temporary files and cpu overrunning the server. The core stability of the forum is being disrupted here.


Please don’t forget that this can easily be resolved by configuring your mail server properly as well.

1 Like

AFAIK my server is configured properly. Certificate name matches smtp host name, STARTTLS on port 587. I’m wondering why I faced the issue?

Thanks for opening a new ticket. Given your understanding, could you shed some light on the combinations of the two variables you pointed out in the YML file - how should they be used for different scenarios?


For example I have only STARTTLS on port 587 and no other ports being used by SMTP for security reasons. Should both the variables be specified in the YML file or just one?


It depends.
If your SMTP server is configured correctly then you shouldn’t need either of them.

But the problem right now is that they are not doing anything at all.

Send me a PM with the name of your SMTP server and I’ll take a look and see if I can find why it’s not working for you.


I have a local SMTP server with no TLS/SSL support and when using StartTls=false it does not work :frowning:

1 Like

Fair point, but it’s not always our mail server. I’m using an internal mail server that is maintained by another group, and so have no control over the certificate issues or the mail server configuration.

That said, for others struggling with this, one option may be to set up your own mail server on localhost and just have it forward mail onward. Then you have control over the mail server that Discourse talks to, and your mail server on localhost can be configured to deal with whatever kind of upstream issues you might encounter. I had done this previously, but removed it at some point since it was simpler to just have Discourse talk to the upstream mail server directly. (Oops.)

1 Like

That’s why the Standard Install recommends third-party mail providers, rather than trying to use an existing or self-hosted solution.

Mail is hard for a multitude of reasons, just because something is working today doesn’t mean it’s correctly configured, only that the misconfiguration doesn’t impact the original purpose.

1 Like

The reason I picked discourse was that it supposed to be easy to install and maintain for a small self hosted deployments.

1 Like

And it is if you follow the recommendations.

If you opt to take a different path it’s not really possible to make any guarantees.

1 Like