We can ask our machines to remind us when to contact prospects, and we can then zip off an informal query or stay in touch in a way that somehow seems warmer than a phone call. This is a boon to recruiting. Recruiters, too, need to recognize that there are degrees of formality, and to choose the one that is appropriate. An introductory contact might best be made in a medium that allows instantaneous, two-way conversation. We call that the telephone, or talking face to face.
Rejection can be tough.
It can be demoralizing. E-mail may make that easier for you, but not for them. It is a brushoff. If someone has taken the time to pull together a hard-copy application, respond in kind. If, on the other hand, someone has applied by e-mail, I have no compunctions about replying in the same medium.