Started getting 'Unknown To: Address" failures

In the Discourse instance I help run, I’ve gotten a number of “Unknown To: Address” error reports recently… I’ve gotten it myself and have gotten a number of reports from users.

In my case, I was replying to a PM. Other cases were people replying to a topic by email and their messages getting rejected.

The weird things:

  • We haven’t made any configuration changes recently, and have used the reply-by-email functionality since we created our Discourse site
  • I don’t see any errors in the raw logs. on “/admin/email/rejected” I see the correct rejections like AutoGeneratedEmailError and UserNotFoundError, but not anything corresponding to the errors I’ve seen and other users have sent me

I’d appreciate any help in figuring out where to look to figure out what’s going on!

Well, it’d be handy to know where these errors are being seen (preferably with screenshots), along with a description of how your system is setup, exactly.

Good point!

We use the standard reply-by-email settings:

But when I replied to a recent PM, I got an error from that reply-by-email address:

We run it on DigitalOcean use SendGrid for email, and have an incoming email address set up on our Google Apps suite. (I’m not sure what else would be helpful on the setup side)


For that bounce, there should be something in Emails -> Rejected. If there isn’t, you’ve got yourself a mystery. I’d start by looking in the Rails logs for the original e-mail, and comparing it against the message that was sent, to see if something along the way is mangling the e-mail.


Yeah, there’s definitely nothing in Emails -> Rejected. I’ll follow those steps you recommend to dig into it, though. Thanks!

@jedc768, I’ve had the same issues with failed Reply by Email emails since upgrading to Discourse v2.0.0.beta1 +4. I’ve seen rejected emails with “Email issue – Unknown To: Address” and " “Email issue – User Not Found”. I even had @nixie investigate with me and we came up empty on a root cause.

I could put together a Google doc with lots of screen shots, Mailgun error logs, and other relevant information to help figure out what’s going on. But before I do, have you discovered what’s going on with your Discourse install?

We haven’t yet - I haven’t noticed any of these errors in Emails -> Rejected, so it’s only if people manually forward them to me that I hear about them.

We’re currently on v2.0.0.beta1 +7 and it does sound like we’re encountering the same phenomenon. The engineers I work with are going to dig into it more next week.

As far as I’m aware, we haven’t had any queries from any of our hosted customers about problems like this, so the problem is less likely to be in Discourse proper, and more in how you’re getting email into Discourse. If you’re both using gmail/gapps via POP, perhaps they’re doing something funky?


That’s good information - thanks, Matt.

We haven’t changed our settings in ages - still using with SSL on port 995. Any chance there’s a new best practice for this?

I’m wondering if it’s still just @JoelZaslofsky and me having problems with this, or if others are seeing this, too?

Indeed. We haven’t used POP3 polling on hosted sites for… well, since about three months before this guide was written.


That explains it! We set up all our infrastructure about a year before that guide came out. :slight_smile: Thanks for the link.