Apparently nearly 500 people have signed up to the service, which stores time-coded messages from the dead on 'encrypted servers'.These messages are only released to a list of recipients after the client has died.
PRHQ director Kizzi Nkwocha, who is leading the account for postexpression.com, says the campaign will - somewhat surreally - target the arguably rather broad audience of 'anyone who is aware that they definitely will die in the future'.
The agency won the work through another client, Guy Goma - the man who was erroneously interviewed live on air when he went for a job at the BBC last year.
One of the staff working on Goma's website also works on postexpression.
The site - which uses the strapline 'death ends life, not a relationship' - will even accept insulting messages.
As Nkwocha says: 'It gives you the ultimate last word.'