How to fix bounce-back emails with Auto-Complete entries
Notice The Auto-Complete
When you start to type out an email you will get a drop down of available contacts.
Delete Bad Cached Entries
If you receive a bounce-back alert from a known good email address, try deleting the cached entry. To do this click on the "X" to the right of the email address in the drop down.
Type Address Manually
After deletion you will notice the drop down list no longer shows the email. Type the email address out manually and create the email as needed. Send the email.