A domain hosted at Microsoft 365 using the e-securemail solution in connector version, can be blocked in the creation of a plan (which has for effect to create a group with mail address) in Microsoft Planner.
Comments on tasks are blocked (indicating that the group is not set up to receive mail) by Microsoft.
Error returned by Microsoft :
There are two ways to solve this behaviour:
Solution 1:
Add an exception in the Send to connector IN and OUT rules, as long as the sender or receiver is internal to the organisation do not route to the ESM connector.
1. Go to your Office space in Exchange and Mail Flow => Exchange admin center rules (microsoft.com)
2. Edit the Send to connector IN rule by adding the exception "The sender" => is "InOrganization".
Then the Send to connector OUT rule
with the exeption "The recipient" => is "InOrganization".
Alternative 2 (recommended) :
We recommend you to use the MX version of e-securemail for a better use of the services.
The recommendations have changed since the last Microsoft 365 updates.
The use of the e-securemail connector services is optimal (as long as they do not contain any additional rules or third party applications) for a basic environment.
Outside of basic configuration or use, a domain may face security policy constraints applied by Microsoft.
For this reason, we recommend the use of MX to avoid the need to apply additional exceptions (when these are possible to be applied).