questions about secure email
I run a web and mail server for a few domains. running with ispcfg3 and according to the perfect debian server howto.
some of the users of a particular domain are using outlook and no matter what I do they are asked about accepting my self-signed certificate. I tried many solutions to import it into their computers but all fail. they are still being asked about accepting the certificate every time they open outlook again.
I have now decided to get a proper certificate but am not sure where to start.
1. any affordable certificate providers you can recommend?
2. will I need only 1 certificate for the server or does every domain need their own?
3. if I need only one, will there be problems since every customer accesses their mail via i.e. mail.domain1.com others via mail.anotherdomain.com, etc?
sorry for these basic questions but I didn't find any good starting point via google to read up on this matter (any links are welcome)