My sendmail configuration contains several rules used to block mail from known SPAM hosts, which may be identified by their IP number or their canonical name. When you run sendmail in address test mode (-bt option), there is no connecting host. However, you can set the appropriate macros by hand for a proper simulation, as in the following example:

$ sendmail -bt
> .D{client_addr}
> .D{client_name}
> check_rcpt 

In this example, the relay host's address and name are set to values that correspond with one of the mail hubs used by; the sender address is also stored in the f macro; and then an address check is performed on the desired destination address. No rocket science, mind you, just stuff that requires a tedious of searching to locate in the infamous Sendmail book, which is why I chose to record it here. Of course now that I wrote it down, I'll probably not forget it again...