Database mail constantly tries to use DOMAIN\Administrator account

So the Title says it all...
We have an 2008 R2 SQL Server that sends database mail to our Exchange 2007 server using a variety of stored procedures. None of the Database mail profiles/accounts use the DOMAIN\Administrator account (well-know accounts such as Administrator cannot use exchange server). What is happening:
In the Exchange server logs there is error 1035(logon denied) followed by 1020(user has valid credentials but is not authorized to use the server) These are expected if DOMAIN\Administrator tries to use the system; problem is, this account ISN'T using the system as far as I can see. SQL Server services and SQL server agent services are all started with DOMAIN\testuser account... I'm stuck.
I have attached the smtpReceive log from the exchange server as well; it shows the denied login but I cannot figure out where it is coming from!
The emails that we EXPECT to be sent are indeed sent; there is just this unsuccessful login even though there is no email going to/coming from DOMAIN\Administrator...

Any insight or help would be greatly appreciated!
Andy