If emailing is beyond the scope of PT, what about a feature to copy the email addresses of the users of a project to the clipboard? Then they could be pasted into an email client.
The transition to PT8 has made me think about this again: when an administrator wants to migrate a project to PT8, they need to inform the users that, if they want to keep seeing the latest version, they need to get the project in PT8; and inform those who can make changes to the project that they must stop doing this before the migration, so and S/R, and not make any changes after the migration.
Some projects have scores of users, and what’s more, the administrator doesn’t have access to the users’ email addresses unless he knows them all by another route. This might be particularly relevant for projects that have more than one administrator: if one admin adds some users and later another admin needs to contact those users, the first admin may not be available to supply the addresses of those they added.