When you mail a letter, do you drive it to the post office and mail it, or just take it to your mailbox and let the postman pick it up?
If it's a birthday card we just put it in our mail box. If it's a bill or anything else that's really important then we take it to the post office.
I usually put it in the mail slot by the wall of mailboxes at my apartment complex. It's a secure place, & I haven't had a problem with anything not reaching its destination.