Problem on sending email to some domain - Error: 451 Temporary local problem, please try again

Question

Hello, 
 we are sending out our emails from our internal mailserver. For some email domains we can everytime a local mail error: 
 ------------ Sophos XG Firewall was unable to send the following mail:

From: d.xxxx@bixxxxxx.de 
MessageID: <f04d4d62-48ca-6740-609f-a011906ba128@bixxxxxx.de> 
Sent on: 2021-01-07 16:54:24

Mail delivery to following recipients failed:

yyy@mohn-gmbh.com - 451 Temporary local problem, please try again!

DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple;
	d=binsack-reedtechnik.de; s=mail;
	h=from:subject:date:message-id:to:mime-version:content-type:
 content-transfer-encoding:in-reply-to:references;
	bh=ram0cpB6DP6WKSqulhSz2oiHpsPc0XDwtm4LPikecdg=; 
 X-Footer: Ymluc2Fjay1yZWVkdGVjaG5pay5kZQ==
Received: from ....
	(authenticated user d.xxxx@bixxxxxx.de ) 
 by mail.bixxxxxx.de with ESMTPSA (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256 bits)) 
 ------------ 
 This error occur also by more special domains. But we can receive mails from this domains. 
 Other domains function well. 
 
 When I look in protocol view, everything seems fine.

We use actually no MTA- modus. 
 
 So there will be no greylisting active . or ? 
 
 Our system: 
 Sopos XG 115 FW: SF 17.5.14 MR-14-1 
 What should I do ? 
 
 Thanks 
 best regards 
 Dirk M&uuml;hlhauser

PhilippRusch · Answer

Hello Dirk, 
 two things: you are posting your XG problem in the UTM specific forum. 
 Second: You are SENDING mails, so greylisting is happening at the receiver's side. There is nothing you can do about this on your side. 
 Whether you are enabling greylisting on your side or not , this doesn't change the symptoms your are watching above. So I think the XG is not the culprit. 
 You should work together with the receiver of your mails, why your mails are getting hit by these mails. 
 Normally, these errors occur when your MX- and/or your reverse-DNS entries are not correct. You should double check DNS configuration for your domain.