I would have initially said a firewall issue but if your co-worker can send fine, that wouldn't seem to be the case at second glance. Hotmail and iCloud both use port 587 for the outgoing email settings, so if 587 was blocked, neither you nor your co-worker would be able to send. Your iPad, is it running iOS 5.0, 5.01, 5.1, 5.1.1? Compare with your colleague the version of iOS and update if necessary, or maybe contact whomever administers the network at your workplace.