To ensure speedy delivery of your snailmail, clearly write the receiver's address on your card or letter. In the case of letters, you should always write a return address on the back of the envelope. This way, the postal service can return any undeliverable items to you.
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Send your goodies through the mail using a flat rate box or a padded envelope. This will ensure that it fits in the letterbox and arrives at your snailmail friend in good condition. Also, use proper packaging materials such as bubble wrap or packing peanuts to protect the items during transit.