>используют ли Exchange и Outlook какой то специфичный протокол для общения
Да. RPC. Но, конечно, можно настоить и на стандартные SMTP-POP-IMAP, но по умолчанию, если в учётке выбрать тип сервера Exchange - RPC.
Network Ports Used by Key Microsoft Server Products
МСExchange Server
Microsoft Exchange Server includes several system services. When a MAPI client such as Microsoft Outlook connects to an Exchange server, the client first connects to the RPC endpoint mapper (the RPC Locator Service) on TCP port 135. The RPC endpoint mapper tells the client which ports to use to connect to the Exchange Server service, which are dynamically assigned. Exchange Server 5.5 uses two ports, one each for the information store and the directory. Microsoft Exchange 2000 Server and Exchange Server 2003 use three ports, one for the information store and two for the system attendant, respectively. Alternatively, Microsoft Outlook 2003 can use RPC over HTTP to connect to servers running Exchange Server 2003. Exchange can also provide support for other protocols, such as SMTP, POP3, and IMAP.