I have synced my On-prem AD with Azure AD. Some user have O365 licensed mailboxes and others who are synced remain unlicensed users. I DO NOT have an on-prem exchange server. Those who are unlicensed are using a non-Microsoft email service (Zoho)
Say, I create an email distribution group called A with members A1, A2, A3 and synced it to the Azure AD. A1 is an O365 user and other two users are unlicensed users (but they have mailboxes in Zoho; MX is pointed to O365 and a connector has been configured from O365 to Zoho and no issue with sending and receiving emails for individual users).
Azure user IDs of A2 and A3 matches exactly to their email addresses in Zoho.
When I send an email to the distribution group A, only A1 receives it. A2 and A3 do not receive it. Checked email logs in both O365 and Zoho. Not even a single entry about an email to A2 and A3.
Further, when I open the synced distribution group in Azure, I can see A1,A2,A3. A1 has his name with the email address, but A2 and A3 is displaying only their names, no email addresses.
In my On-Prem AD, I have already set proxyaddresses attribute for A2 and A3 (format - SMTP:A1@domain.com).
What's the solution for this ? I need all unlicensed users to have their email addresses synced correctly into the Azure AD and must be able to include them into the email distribution groups to receive emails.