No invitation email is sent when external users are invited to a private Azure DevOps project

Today I was confronted with an unexpected behavior of Azure DevOps Services. An external user got invited to a private Azure DevOps project by following the steps below.

1. Open a private Azure DevOps project
2. Click the Invite button in the upper right corner
3. Enter email address of external user
4. Select the team the user should be added to
5. Click Add

Unfortunately the corresponding user did not receive an invitation email (spam folder got checked) and therefore could not get access to the Azure DevOps project.

After a short research I came across the following thread in the Developer Community forum:

https://developercommunity.visualstudio.com/t/the-invite-user-button-in-azure-devops-service-tea/1014793

This seems to be a known issue, which can be circumvented as follows:

1. Go to Organization Settings
2. In the left menu select Users
3. Enter the email address of the corresponding user in the filter pane on the top
4. Hover over the corresponding user, click on the three dots at the right side and then select Resend invite
   

To avoid these additional steps, invite external users directly in organization settings by clicking the Add users button (see screenshot above).