It depends on how you are connecting to Exchange Server.
Is this withing the same site in the domain? IE is this workstation geographically local to Exchange? this only matters for FW configuration but still a worthy question to ask.
What protocol are you using to connect to Exchange? MAPI/POP/IMAP?
Depending on what protocol you are using will determine what port. For example, MAPI uses RPC over port 135 to establish a connection and then negotiates a unique connection over a different port with the client for connectivity.
Feel free to PM me, I'm an Exchange engineer/technician for my company.