Fetchmail will work, but is not necessary if you are retreiving only one external email.
To see if SME is getting your email, enable webmail on the server, and log in to your webmail acount.
The fetchmail program you are refering to is for SME 6.0 and 6.01 You should use the one Ray Mitchel refers to.
You will need to set your email client to use ssl. Pop3 is the standard ssl port, and smtp is port 465. You will need to set that port manualy, and do it after you place the tick in the ssl box, otherwise it will change back to 25 and you will have to set it again.
SME will connect to your pop3 account in the normal way if you have entered you account information correctly.
You should not have to route any ports. Are you using SME with a router?
I am not shure about IMAP. I only play with POP3