Odd email delivery issue
Problem reported by Scot Desort - 4/5/2024 at 10:36 AM
Submitted
So I have come across a strange issue sending email to a particular email address. This email address is one for the Intercom helpdesk system. Email coming into smartermail is being forwarded to IntercomMail for the purposes of creating a ticket. I have sent the same test email from various email addresses, and also tried with 2 email clients (Outlook desktop and Apple mail on a mobile device). The results are always the same:

[2024.04.05] 10:26:28.283 [23000731] Attempting to send to MXRecord 'inbound-smtp.us-east-1.amazonaws.com' ip: '54.164.173.191'
[2024.04.05] 10:26:28.283 [23000731] Sending remote mail to: redacted@intercom-mail.com
[2024.04.05] 10:26:28.283 [23000731] Initiating connection to 54.164.173.191
[2024.04.05] 10:26:28.283 [23000731] Connecting to 54.164.173.191:25 (Id: 2)
[2024.04.05] 10:26:28.283 [23000731] Binding to local IP X (Id: 2)
[2024.04.05] 10:26:28.309 [23000731] Connection to 54.164.173.191:25 from X:53137 succeeded (Id: 2)
[2024.04.05] 10:26:28.341 [23000731] RSP: 220 inbound-smtp.us-east-1.amazonaws.com ESMTP Amazon SES BJO8o3LwJ92BQgb7JBE1
[2024.04.05] 10:26:28.343 [23000731] CMD: EHLO redacted
[2024.04.05] 10:26:28.388 [23000731] RSP: 250-inbound-smtp.us-east-1.amazonaws.com
[2024.04.05] 10:26:28.388 [23000731] RSP: 250-8BITMIME
[2024.04.05] 10:26:28.388 [23000731] RSP: 250-STARTTLS
[2024.04.05] 10:26:28.388 [23000731] RSP: 250 Ok
[2024.04.05] 10:26:28.388 [23000731] CMD: STARTTLS
[2024.04.05] 10:26:28.420 [23000731] RSP: 220 Ready to start TLS
[2024.04.05] 10:26:28.665 [23000731] CMD: EHLO redacted
[2024.04.05] 10:26:28.701 [23000731] RSP: 250-inbound-smtp.us-east-1.amazonaws.com
[2024.04.05] 10:26:28.701 [23000731] RSP: 250-8BITMIME
[2024.04.05] 10:26:28.701 [23000731] RSP: 250-STARTTLS
[2024.04.05] 10:26:28.701 [23000731] RSP: 250 Ok
[2024.04.05] 10:26:28.701 [23000731] CMD: MAIL FROM:<redacted>
[2024.04.05] 10:26:28.732 [23000731] RSP: 250 Ok
[2024.04.05] 10:26:28.732 [23000731] CMD: RCPT TO:<redacted@intercom-mail.com>
[2024.04.05] 10:26:28.795 [23000731] RSP: 250 Ok
[2024.04.05] 10:26:28.795 [23000731] CMD: DATA
[2024.04.05] 10:26:28.826 [23000731] RSP: 354 End data with <CR><LF>.<CR><LF>
[2024.04.05] 10:26:28.826 [23000731] Exception: Object reference not set to an instance of an object.
[2024.04.05] Stack:    at MailService.RelayServer.Clients.SMTP.SmtpClientSession.SendData()   at MailService.RelayServer.Clients.SMTP.SmtpClientSession.GiveData()   at MailService.RelayServer.Clients.SMTP.SmtpClientSession.StartProcessing(String sessionId)10:26:28.826 [23000731] CMD: QUIT
[2024.04.05] 10:26:33.857 [23000731] Attempt to ip, '54.164.173.191' success: 'True'

And while it shows "success:true", the email isn't delivered. It DID eventually get delivered after several re-tries. Not really sure why one attempt would fail and another would succeed, without an error being thrown from the receiving server.



Douglas Foster Replied
Which Build?
Scot Desort Replied
Sorry. 8818
Sébastien Riccio Replied
Strange issue indeed.

According to the log timestamps I would say it looks like the latest response from the remote mail server "354 End data with <CR><LF>.<CR><LF>" is triggering an exception.

Maybe SM doesn't like the <CR><LF>.<CR><LF> stuff in the server response when it answer to DATA command.
Hypothetically, maybe it tries to parse the content between <> as e-mail addresses and this could trigger an exception ?


[2024.04.05] 10:26:28.826 [23000731] RSP: 354 End data with <CR><LF>.<CR><LF>
[2024.04.05] 10:26:28.826 [23000731] Exception: Object reference not set to an instance of an object.

I guess at this point only a SM dev could answer this one though...

Kind regards
Sébastien Riccio System & Network Admin https://swisscenter.com

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