French phrase for returning post to sender

[HoneySuckleDreams]

Hi

I once knew what to put on an envelope to "return to sender", but i've forgotten. we have a letter for someone that does not live here anymore and it looks like an important tax thing.

I seem to remember it's a 4 letter acronym, but can't for the life of me remember what it is.

thanks in advance

[Nell]

See here - http://www.wordreference.com/enfr/sender

[Will]

I don't know an acronym, but there will almost certainly be one - the French cannot exist without them.

If it's something important I would be rather inclined to write in full "Retour à l'expéditeur" so that it is perfectly clear what you mean.