Question
Is it possible to change the webmail subdomain link URL at Domains > example.com > Mail > Mail Accounts to a custom one?
Answer
Such functionality is not implemented in Plesk yet, however a feature request for it already exists in the Plesk User Voice portal, due to which you may view and vote for it on the following link:
Add possibility to change default webmail. subdomain to custom – Your Ideas for Plesk
Top-ranked suggestions are more likely to be implemented in future versions of Plesk.
As a workaround, you may configure a single specific webmail URL or subdomain (which must be hosted on the Plesk server) to be used by all domains on the server via custom configuration templates, as explained in the following article:
How to redirect webmail of all domains to a specific webmail URL in Plesk for Linux