Are you sure the message is not too large to be sent by your ISP?
Also, virus scanners which integrate themselves into Outlook are also a know
cause of this. Disable/uninstall this integration and try again.
See http://www.msoutlook.info/question/20
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments. After that, you can post your question and our members will help you out.