Sending an e-mail from word 2000

I have a user in our organisation who has problems when sending e-mails from word 2000. The problem is it seems to be intermittent.

He creates a word document and clicks the send option after inserting the users e-mail address. Some of the mails go and some don’t.

I have checked that Outlook is the default mail and that word is the default editor and also that the send document as attachment is checked within the tool > options > general within word.

What could the problem be andone got any ideas?

Really appreciate help with this matter. Thanks!