I have McCaffee Firewall installed. I also use Act by Symantec for my
contact manager and to send email. Act uses a proprietary email
client. I can access my email direct through the Internet also.

My email account is hosted by Interland who is the mega giant for web
and email hosting. I have noticed that for months I am not receiving
all my email. Today I looked at my firewall properties and I noticed
that it said "Actemail.exe  Grant access only to outgoing mail"
But the fact is thta I am receiving about 20 emails per day but I 
know for a fact that I am missing others.
But on the other hand, I always check my mail first on the Net before
I download through ACT.
Question: How would the Firewall block on my incoming mail really
affect the incoming mail?

Also, Interland has been black listed by many servers.
Question: Could this blacklisitng affect my incoming mail?

Bottom line question: Why am I not receiving all my email. It is
somewhere in cyberspace.

Possibility: you are using the virus scanner, too. Maybe you have
checked the worm-protection (so the scanner will disable the mailing
automaticly) at the options.

Maybe Interland is using some sort of mail-killer software such as SpamAssassin