Yes, PoliteMail will run in Citrix and Citrix XenApp environments
Each user/seat still requires a PoliteMail for Outlook license.
Users login to their Citrix profiles, and access PoliteMail through the PoliteMail for Outlook desktop client software, which must be installed for each user.
PoliteMail can provide an MSI that can be installed on Citrix.
The client software must have network access to the PoliteMail Server.
If PoliteMail is installed for the entire Citrix machine for all Outlook users, then all Outlook users would have access to PoliteMail. For those Outlook users without PoliteMail for Outlook licenses, the add-in must be disabled.