A “love letter” is a playful name for a letter from the postal services which basically states:
We seized your goodies, but don’t have the time/money to build up a case against you; and/or you didn’t order enough for us to be too concerned. You lucked out bastard. Don’t do it again, we are watching your address. Sincerely, LEO/Post Office/Postal Inspector
International Seizure Letters
Customs agencies around the world, including US Customs, frequently send “love letter” seizure notices to recipients of international mail with small amounts of suspected illegal drugs inside. These seizure letters are usually real.
Once you get one of these love letters, consider that address burnt. Do not use it again as a delivery address for contraband. PSA: US Customs keeps a record of all seized packages that were going to your address.
It is possible to receive a fake international seizure letter.
Domestic Seizure Letters
It is very, very uncommon to get a domestic seizure notice for seized items sent from inside a country for delivery to the same country. The usual protocol when illegal drugs are found in domestic mail is to conduct a controlled delivery and arrest the intended recipient. Normally any seizure notices of this kind are simply clever scams by unscrupulous vendors. This applies especially in the USA where, 99% of the time, any seizure letter you receive for a domestic (US to US) drug order is totally fake. The only time US Postal Inspectors send seizure letters for domestic items is when they have seized cash.