- Plesk for Linux
There are two domains in a subscription (in case of Web Pro or Web Host editions), or several domains in case of Web Admin edition.
Webmail is set to None for the main domain of a subscription (in case of Web Admin edition, for the first domain on the server).
If disable mail service on a main domain of the subscription at Domains > example.com > Mail Settings > uncheck Activate mail service on this domain > OK , then webmail is set to None for other domains of this subscription (in case of Web Admin edition, on all domains other than the first one).
This is Plesk bug with ID #PPPM-6036 which is planned to be fixed in future Plesk updates.
As a workaround, disable mail service on the main domain of the subscription:
Go to Subscriptions > example.com > Mail > Mail Settings ( Mail > Mail Settings in case of Web Admin edition) > select necessary domain on the left to its name > Activate/Deactivate Services > select Disable in the Mail service > OK .