Thanks to all who helped! Although Maggie's post wasn't the exact answer, it sure pointed me in the right direction, and I should have been MORE PATIENT in waiting for my changes to propagate.
As for the "not getting mail from outside"... I was testing from ,my YAHOO account, and my test messages kept getting bounced. THEN I noticed I had received an "outside" message (from somebody NOT on MSO365) and had to rethink.... it turns out I was spelling BRENHAM wrong in the email address.
Yeah, I feel pretty stupid.
HOWEVER, I believe everything is working correctly, and I DO appreciate the help.
I believe this incident can be considered CLOSED.
Pastor Billy