I was actually wondering that myself, so I checked. The answer is yes, well it worked for me anyway.
I have a Server 2003 Ent that is a member of a windows 2000/2003 domain. I am running MDaemon 7.2.1 (latest version) under the local system account. I did some searching through the help file for mdaemon and found out that you can import accounts from a domain if you wish or if you already have the accounts, you can just type in "\\DOMAIN" into the password field of the account; without the quotes of course. Notice the statement that says "not using dynamic NT Authentication" changes after you type in the "\\". The downside appears to be that the account name in mdaemon must match the account name in active directory, well from what i have read so far anyway. If there is a way to perform account name mapping I would love to know.
Cheers
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Josh
CCNA, MCSE 2003(in progress)