1) Faster Delivery Mostly Instant.
2) Easy to Access and reply instantly
3) No paper wastage
4) Easy to store and retrieve
5) No Clutter on your work or home desk with bills and other letters.
6) Almost all companies offer you email updates which you get much faster then the letter they send you via post.
Email Security is basically related to letting your password known to others. You should never let other know about your password. Otherwise Emails are quite safe.