This question has no relevance to this *Frontpage* newsgroup (the issue is
not a Frontpage problem).
You have to install (or possibly reinstall) your email application, such as
Windows Mail, Outlook Express, Eudora or Firebird or Outlook or whatever.
The email application you use is your default mail client.
If there are two such programs eg Windows Mail and Eudora (I for one use
Outlook 2007 for email and OUtlook Express for Newsgroups) - my default
client (for mail) is Outlook 2007), then you need to choose one or other as
the default.
When you start either email program, it should popup a box asking if you
want it as the default (a similar thing occurs if you have multiple browsers
on your system, when you start it/them asks if you want it as the default
browser).
In this case there seems to be a problem with your email program; a good
idea would be to check and reinstall it if necessary.
To install the email program you need to download it (e.g. freebies like
Firebird (from makers of Firefox))or purchase such as MS Office/Outlook and
load the program from the provided disk.
Andrew.