How to get only the users that have a mailbox in Azure active directory using Microsoft Graph API?

Question

I am using Microsoft Graph API to read emails (/users/{id | userPrincipalName}/messages) in the mailboxes of the users in my Azure active directory. I have noticed that for some users, I get this error:

HTTP error: 404
Error code: MailboxNotEnabledForRESTAPI or MailboxNotSupportedForRESTAPI
Error message: REST API is not yet supported for this mailbox.

Upon investigation, I found out that these users do not have a valid license and also don't have a mailbox attached to them. Ideally, I would like to only fetch the users that have a mailbox enabled. I tried checking the assignedLicenses property of each user and only fetch emails for those users that have a valid license assigned to them but, I'm not sure if this is a reliable method as users might have some other license and still not have a mailbox enabled.

Can someone please suggest a straightforward way to only fetch the users that have mailboxes attached? Any help or hint shall be highly appreciated.

Answer 1

I don't see much options from Microsoft Graph perspective. Definitely checking the license is one good way, but you may not have much options with that. Being said that i see the following options,

• you may need to use mailboxsettings API call of the user. This way you can get and update the mailbox settings of the user.
• Also you can use Get-mailbox Exchange Powershell cmdlet to validate the same as well.