I have one contact/email address that when i enter him/it into the address line(s) of a message, it has a '?' in front of the address.  It is also highlighted in yellow.  Can someone help explain why this occurs.

Thank you.

Rick
As I go to send a new email and type in a contact name, none of my contact email address's come up.  So I have to do a search, copy and paste to enter into the address line.  This is a pain and I will not do this for long before I establish a new account with another provider.  Why is this happening?
When I reply to a message, my reply is delivered to my inbox, addressed to me even though my address was not in the recipient's address line.  Normally, replies should just go into my Sent box.  How can I prevent this?  This has begun happening only recently.
I'm trying to send an email but can't get the cursor to move around the site.  Then the cursor just quits flashing (disappears).  Also the system won't let me use the 'CC' or hidden address line.  And now even the current emails are not loading.  I've signed out and signed in again but that doesn't help... the system is still not responding (and it doesn't have anything to do with 'calendar').
When filling in the "To" line of an email it used to auto fill with matching address, now it goes into perpetual search mode and doesn't fill in the address.  What's up with that and how do I fix it???
Autofill has stopped on my address line in outlook for mac.  installed software updates yesterday but not sure the two are connected.  help me repopulate so address options automatically pop up when writing an email.