My company is going to be receiving emails from another company who has asked to ensure that we can receive secure emails and that our exchange 2003 system is capable of supporting TLS.
As mentioned above we have an Exchange 2003 server (just one server). I have a certificate installed to access our email through Outlook Web Access (and access them through IPhone's).
Would I need to buy more certificates for 5 users on my domain who are going to receive these secure emails from this external company. If so do I need to install the certificates onto the 5 users PC's.