Have you ever sent an email you later regretted? I sure have. Email may be the crudest form of communication ever invented. It lacks nuance, warmth, interactivity; but it is irretrievable and can be proliferated through forwards to anyone anywhere. The following biblical passages come to mind.
"Let all things be done for building up" (1 Corinthians 14:26). All things in all aspects of the church, without one exception. If then an email is not positive, constructive and uplifting, it's better to pick up the phone -- or better yet, actually get with the other person. That would not guarantee edification, but delicate conversations via email stand little chance of success.
"Whoever restrains his words has knowledge" (Proverbs 17:27). Even when one does exercise restraint in composing an email, it just doesn't come across as restraint to the person receiving it. Email seems incapable of communicating restraint, even with good intentions. Wise restraint may require silence. But if silence is not an option and one must risk the possible "feel" of lack of restraint, then the least desirable medium is email.
"We pray most earnestly night and day that we may see you face to face" (1 Thessalonians 3:10). Paul never prayed trivial prayers. He invested his earnest, night-and-day prayers only for those few things that matter most, like seeing one another face to face! Face to face conversations have an almost mystical power to soften, to win, to spread everything honoring to Christ and delightful to us.
God didn't send us an email. Well, maybe the tablets of stone on Sinai came close. But the greatest communication from God was when the Word became flesh and dwelt among us and we beheld his glory (John 1:14).