Problem with sending out Mails to specific receivers

Question

Dear Support! 
 We have problems sending out mails to a lot of receivers and keep getting the following notification: (... means sender/receiver information) 
 Sophos UTM was unable to send the following mail: 
 ---------------------- 
 From: . .. 
 MessageID: ... 
 Sent on: ... 
 
 Mail delivery to following recipients failed: 
 
 . .. - 451 Temporary local problem, please try again! 
 itself 
 6.227.170] 
 250-SIZE 20971520 
 250-8BITMIME 
 250 XXXA 
 LS 
 250 XXXA 
 TTLS 
 250 XXXA 
 
 It would be great if we could get some help in this case. 
 Thanks in advance

sachingurung · Answer

Hi Sheriff,

Thanks for the update, what do you see in the log viewer > Email logs, when the mail is bounced back?

Are you able to telnet mail server's public IP address from an external network? If not, please check the TCPDUMP and PACKETCAPTURE for the outside user’s public IP on port 25.

If the telnet is successful, you can check the SMTP session from the Mail server telnet session and try to send an email from the telnet session itself.

Telnet to XG and go to option 4. Device console; and execute telnet <mail server IP> 25.

If you receive "Trying <mail server IP address> message means XG is not able to communicate with Mail server through port 25. And if you receive a message like "Sender Unknown" or "Relaying Denied" means XG is not able to forward mail using the above configuration.

Thanks