Mail.app not downloading from server correctly
I am using Mail.app on 10.4.9 with a Mac.com email address setup and am having problem receiving emails from just one person - that's right only one sender.
What happens is, the person sends the email and it arrives at the webmail interface (i.e. I can view the email using Safari) but the emails are not downloading to Mail.app like all others i receive, I have to login to .Mac webmail to read the emails this persons is sending to me.
I have noticed that once the emails have been read on WebMail, Mail.app will then download them to the Inbox and mark them as read.
I have tried synchronising the account and rebuilding the mailbox but am still not able to get Mail.app to download these emails.
Thanks for any help.
Gary
PowerBook G4 1.25GHz FW800, Mac OS X (10.4.9)