Fixing 502 Bad Gateway Nginx

Hi,

I am coming from youtube video https://www.youtube.com/watch?v=obRxID54H14&list=PLEw57Zr9GItiqmK7RJgqvAr5593HGmu7Q&index=2&t=219s about fixing 502 Bad Gateway Nginx.

I have a Postal SMTP server installed on Ubuntu 18. For a reason I dont know, the server drops and shows 502 bad gatways nginx.

I have followed your debug on youtube and I found this proxy pass message. A backend service that is running on port 5000.

}

    location @puma {
        proxy_set_header X-Real-IP  $remote_addr;
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto https;
        proxy_pass http://127.0.0.1:5000;
    }

I was not able to discover what service it was.

By chance I tried to start postal service by:

Sudo postal Start

The server returned

Started Procodile supervisor with PID 1227

I tried to access the server from the browser after and it worked!. However, I am not able to send emails event though I am 100% sure of the credentials.

My next step was to debug the SMTP service. and Here are the test returns:

Connected to smtp://postal.mylinkys.xyz:25/?starttls=when-available
<< 220 postal.mylinkys.xyz ESMTP Postal/LRL1GT
>> EHLO [172.31.10.74]
<< 250-My capabilities are
<< 250 AUTH CRAM-MD5 PLAIN LOGIN
>> AUTH CRAM-MD5
<< 334 PDA0Zjg0MWMzZDIxMGRhM2RjMGEzQHBvc3RhbC5teWxpbmt5cy54eXo
>> ZS5jb29rbGVyLmNvbSA2MWUyYjJhNzU1Mzc5NjJhMjRmMzI2MTVmYTI4MmE4Zg==
<< 535 Denied
>> AUTH PLAIN AGUuY29va2xlci5jb20AU3RDSlU5MjBhNTRjZkF1a09OOVZPTFNP
<< 235 Granted for mailing-system/smtp
>> MAIL FROM:<care@XXXXXXX.com>
<< 250 OK
>> RCPT TO:<mr.XXXXXX@gmail.com>
<< 250 OK
>> DATA
<< 354 Go ahead
>> From: care@XXXXX.com
>> Date: Tue, 29 Dec 2020 10:08:41 퍍
>> Subject: SMTP test from postal.mylinkys.xyz
>> Message-Id: <ZY1RYKPKKCU4.DT6UMYJYPLES3@WIN-AUIR3RRGP88>
>> To: mr.XXXXX@gmail.com
>> MIME-Version: 1.0
>> Content-Type: multipart/alternative; boundary="=-YDkWWl67JIrkb99tqr5XXA=="
>>
>> --=-YDkWWl67JIrkb99tqr5XXA==
>> Content-Type: text/plain; charset=utf-8
>>
>> Test message
>> --=-YDkWWl67JIrkb99tqr5XXA==
>> Content-Type: text/html; charset=utf-8
>> Content-Id: <ZY1RYKPKKCU4.4BNJ84W1Q29U2@WIN-AUIR3RRGP88>
>>
>> <b>Test message</b>
>> --=-YDkWWl67JIrkb99tqr5XXA==--
>> .
ERROR: The SMTP server has unexpectedly disconnected.

I was not able to send a message. So I tried to restart the whole server.

After the server restart I got again the 502 Bad Gateway Nginx error. I fixed it again using the command above and posted here asking for help.

Any ideas on what to do ?

Thank you very much