O365 Group and Distribution Group Cannot recieve Email from External

Occasional Contributor

Created a Group in O365 and also a Distribution Group in O365. We have a Hybrid environment.


Cannot Email from External Email Address


This is the Error


This is the Email Security Gateway at host webmail.domain.com.

I'm sorry to inform you that the message below could not be delivered.
When delivery was attempted, the following error was returned.

<Test0365Group@domain.com>: host IP ADDRESS said: 554 5.4.6 Hop
    count exceeded - possible mail loop (in reply to end of DATA command)

Final-Recipient: rfc822; Test0365Group@domain.com
Original-Recipient: rfc822;Test0365Group@domain,com
Action: failed
Status: 5.4.6
Remote-MTA: dns; IP Address
Diagnostic-Code: smtp; 554 5.4.6 Hop count exceeded - possible mail loop

3 Replies

As the NDR message suggests, you probably have some incorrect setup with your mail flow, causing a loop. As you haven't provided any details with respect to where the MX record point at, how connectors are configured and so on, we can only advise you to check your configuration. You can always open a support case to get this properly investigated.

I just sent a Private Message to Michev

We have a Barracuda Device and mx records points there and Barracuda will accept emails from both.


Only O365 Groups and DG has issue. Cannot recieve emails from pn-prem users and external users.

O365 users can sent emails

@Biju DanielsHi there, Did you find a resolution?

I am in the same boat. My mail flow is fine for On-Prem user to 365 users/shared mailboxes but I get an NDR for mail loop when an on-prem users sends an email to a 365 DL or Group.