Go to {1}.{0}2. Open the Exchange admin center.{0}3. Under recipients, click mailboxes.{0}4. Select this user: {2}. If you ...

1. Go to {1}.{0}2. Open the Exchange admin center.{0}3. Under recipients, click mailboxes.{0}4. Select this user: {2}. If you can't find this user, check to see whether they have the correct license and that it's not expired.{0}5. Edit this user. Under mailbox features, make sure email connectivity protocol {3} is enabled. (Note: you'll have to scroll down in the dialog box to see this setting.)