One of my users has had a few issues with bounce back messages in the last
week or so.  She has received most of them because the other persons emails
could not handle the size of the attachments she was sending.  

The problem that I am having is that when she gets a bounce back the
person's email address that she is sending the email to is erased from her
nickname file.  So, when she has to resend a message she has to look it up
and retype it in.

Is this normal?  Is there an option to uncheck/check so that this doesn't
happen?

Thanks.