5.1.1 <[email protected]>: Recipient address rejected: User unknown in virtual mailbox table

When you see an error similar to the one above, this may be because you are trying to send an email to a domain on your server but that uses an external mail service.

What happens is Plesk will try and deliver this locally because it recognises the domain is enabled on the Plesk panl.

To resolve this you simply need to disable the mail service:

Plesk 12 (and above)

1. Log into Plesk

2. Select the domain you're sending to from the domains list.

3. Click on the "Mail" tab

4. Click on the "Settings" tab

5. Select the checkbox for the domain from the list

6. Click the "Activate/Deactivate Services" button

7. Change the drop down option to "Disable" and click Ok.

Plesk 11.5 (and below)

1. Log into Plesk

2. Select the domain you're sending to from the domains list.

3. Click on the "Mail" tab

4. Click on the "Settings" button

5. Untick "Activate mail service for this domain" and save the settings.

Once completed you will find that mail will deliver to external servers correctly.

Plesk 12>

1. Log into Plesk

2. Select the domain you're sending to from the domains list.

3. Click on the "Mail" tab

4. Click on the Settings tab

5. Select the domain from the list

6. Untick "Activate mail service for this domain" and save the settings.