C# - Add A Web Interface To A Server?

Question: I have a mailserver written in C# and want to add a web-interface.Now the way I see it, there are two possibilities:

1) Somebody want's to integrate the mailserver on his own webpage/webapp --> needs WebService interface

2) Somebody wants to access the mailserver via a web-interface, e.g. on localhost for configuration, but maybe also for writing and reading email.

What's the best way to unify these 2 demands?I mean with 2), the mailserver basically needs his own webserver, listening on port 80 or n, where it displays a page that e.g. ideally uses the WebService to integrate the webserver funcionality into the integrated webserver-webpage.But said integrated webserver should not interfere with an ordinary webserver,if running on that machine.Also there is the problem of ports and firewalls on the client side and in corporate networks.