You might want to direct them to their Settings > Advanced Settings > Auto-Complete 
This will allow them to delete the entry that is causing the misspelled email address.

Hi Andrew!

 

I hope I understand you correctly. I believe you're talking about the incorrect email address auto-populating in the drop down list when entering the To field in a new email, right? This can easily be corrected.

 

Have your user go to Settings > Advanced Settings > Auto-complete. This is a list of all GAL entries and any email address that the user has sent to. Find the entry, right click and choose Delete. The email address should no longer appear in the list of suggested email addresses when composing a new email.

 

Let me know if this is what you were referring to and I'll mark this thread as Answered.