Situation: The client created distribution group for sending emails to external customers in Office 365. However, the external customers don’t receive the email from the group email.
Troubleshooting: By default, only senders inside your organization can send messages to distribution group.
If you check Trace email and you will find the following error: “The message was sent to the following group, which doesn’t allow messages from external senders”.
To fix the problem, Login Office portal. Go to Exchange admin center.
In Exchange admin center, click recipients.
Then click on groups
Highlight the group, which has a problem to send email to outside. Then click Edit icon.
Click on delivery management and check Senders inside and outside of my organization.
Click Save to save the settings and test it.
Please view this step by step video:
