Unable to set Smartermail as default mail server: Unable to assign port to IP address

Symptoms

Unable to set SmarterMail as default mail server due to an error:

Error: Unable to set SmarterMail Server 203.0.113.2 as the default Mail Server: defpackagemng failed: Unable to assign port to IP address.
Reason:
Unknown IP Address: 
(Error code 1)

OR

 Error: Unable to set SmarterMail Server as the default Mail Server: defpackagemng failed: AssignPortToIP(203.0.113.2) failed: Error code -2. Error message: Unknown IP Address:
at (SMSvcUtil::checkActionResult line 66)

Cause

MailEnable was not properly stopped.

Resolution

It is required to stop MailEnable completely in order to activate SmarterMail. For that:

1. Log into the server via RDP.
2. Open Plesk Services Monitor from tray and stop all services of MailEnable.
3. Try enabling SmarterMail once again.
4. If the step above did not help, do the following:
   1. Open registry by typing regedit in the CMD.
   2. Change HKLM > Software > Wow6432Node > Plesk > PSA Config > Config > MAIL_PROVIDER_DLL parameter with path to Plesk smartermailprovider.dll library, for example C:Program Files (x86)ParallelsPleskadminbinsmartermailprovider.dll
   3. In HKLM > Software > Wow6432Node > Plesk > PSA Config > Config > Packages > Mailserver set Default to
smartermail

   4. In Tools & Settings > Server Components click Refresh button
5. Try adding Enabling SmarterMail once again.