Help with the "?" in the emails

I know this has been addressed before, but I can't find the solution in the records. Please, what do I do to remove the "?" from the words in the emails? I use a Mac computer and I've looked all over my preferences for the solution. If you will please tell me where to find the directions for eliminating the "?'s" it will make my life easier, and my translations much clearer, even though they are quite comical at times.

Thank you for revisiting this problem and helping me find the solution.

Linda