Discourse version at localhost: NOT FOUND

Installation
1

Discourse with Proxy nginx. Site worked including email, but emails are no longer sent without log error in discourse. Trying to trace the problem down, I found

========================================                                             
Discourse 2.7.0.beta1                                                                
Discourse version at irusweg.de: Discourse 2.7.0.beta1                               
Discourse version at localhost: NOT FOUND                                            
==================== DNS PROBLEM ====================                                
This server reports NOT FOUND, but xxx reports Discourse 2.7.0.beta1 .        
This suggests that you have a DNS problem or that an intermediate proxy is to blame. 
If you are using Cloudflare, or a CDN, it may be improperly configured.

I am aware that this is not a Discourse problem, but rather one of proxy configuration. Nevertheless, any hint would be helpful.


For a robust test, get an address from http://www.mail-tester.com/                                
Or just send a test message to yourself.                                                          
Email address for mail test? ('n' to skip) [admin@xxx.de]: d@mymail.de       
Sending mail to 
Testing sending to xxxxx using myserver:587.                        
= ERROR ========================================           
                                    UNEXPECTED ERROR                                              
                                                                                                  
500 5.5.1 Invalid command
2

If your site works you can ignore the proxy error.

The other error is also unhelpful, as the tool is useful only for the most common problems like a login issue.

Are there logs at the mail server? Is it receiving mail?

Has something changed since when the mail was working?

3

Thanks for your comment on the proxy error. However:

  • I can sendmail from the host without problems
  • After installing a ephemeral sendmail in app, trying this inside the app container gives the following:
echo "Subject: sendmail test" | sendmail -v mymail@mymail.de
... Connecting to [127.0.0.1] via relay...
... Deferred: Connection refused by [127.0.0.1]

Any hints where too look further would be appreciated.