issue with comments - the group isn't set up to receive messages

[pschoettler]

There is an issue for all of our M365 users with using Tasks by Planner and To Do in Teams. We use M365 with Exchange Online and Teams licenses.

We create tasks in Teams. Each task has a comment box where text can be entered. When a comment is created, the user receives an e-mail with the error message:

the group isn't set up to receive messages from user's email address

It looks like an authorization problem, because comments fail for each user, even the creator of the task. On the other hand the app Planner shows a hint that a new user interface for Planner will be available shortly.

Any help is appreciated.

[#2]

The group's setting to allow emails from external addresses won't help, because each user is from our M365 tenant.

[#3]

Can you try sending email to the problematic M365 Group from your mailbox and check if the email is delivered?

[#4]

@Santhosh Balakrishnan 

when I send an email to the Teams' email address, I receive the same type of undeliverability report.

[#5]

@pschoettler 

I have not seen this error in our use. Would it be possible to check sending email from another user to this same Teams email address and see it it works? This will help to know narrow down the problem. Else, have to raise support ticket with MSFT to get it resolved. 

[#6]

I have tested it with a another user of this Team and still the same kind of undelievery report is received.
Is creating a comment the same as writing an email to the group?

[#7]

Finally we found the solution for this issue.

First, we redirect each internal mail to our antispam and mailarchiving solution (mail flow rules and connectors). 

Second, we activated a security feature in Exchange that external emails to Teams groups are blocked.

Writing a comment in a task is regarded by Exchange as an email to the Teams group. Because this email of the comment is (somehow) redirected to our mailarchiving solution and back to our Exchange online, this email is blocked by the security rule.

When I add an exception for the Teams group to the mail flow rule for internal mails, the comment does not disappear anymore and no NDR mail is sent to the creator of the comment.