From time to time I get an entry in the security log that is headed as
Checking for rejected mail host.  In the current security log I have one
entry that says something like

Checking for rejected mail hosts: (the <someaccount> is to protect the
guilty. dunno why, but just in case)
2 <someaccount>@yahoo.com

I have Sendmail 8.9.3/8.9.3, and in my access.db I have told it to reject
from yahoo.com (That also happens to be the rejected host, as well), but
I've gotten a few others (maybe one or two) a while back before I even found
out about the access.db file.

What does it mean, other than the obvious?  The obvious meaning that I tried
to send email to that account from my FreeBSD system.  I never send mail
from my own system through sendmail, that I'm aware of.

Any insight on this is greatly appreciated.