(1) Any letter can be sent to one of the four mailboxes at will. There are four ways to send three emails at will, so * * * has 4*4*4=64 ways to send them. Any email is put into mailbox 2, and the remaining two emails are put into mailbox 1, 3, 4. There are 3*3=9 ways. Mailbox 2 can put any of the three letters, so there are 3*9=27 different ways to put only one letter into mailbox 2. So the probability is 27/64.

(2) The method of each letter is A43=24, so the answer is 24/64=3/8.