That's a known design shortcoming with Windows Mail.
That, and many other things, have been fixed in the replacement
program, Windows Live Mail:
http://get.live.com/wlmail/overview

--
Gary VanderMolen, MS-MVP (WLMail)


"New Vista User in E PA" <New Vista User in E PA@discussions.microsoft.com> wrote in message
news:944023C3-B55B-46E3-8754-1E6A12F845EB@microsoft.com...
> In Tools-Options-send tab I have checked "automatically complete e-mail
> adresses " , but it does not consistently complete e-mails adresses once i
> start typing. Sometimes it works sometimes it doesn't on adresses in my
> contacts list.