To keep the flow going I send Ryosuke Cohen an enveloppe every two weeks. That way the Brain Cells as a reply do come in. I am currious if he reaches the 1000th issue. That is only a few years away, but a year in mail-art is a costly one with the current postal rates.
On the envelope I use an artistamp that Mars Tokyo sent me. They were for the 25 years celebration of the IUOMA. I am using them on my outgoing mail. Seems more fitting then just archive the complete sheet in the collection. With this passing on more people will see it. With archiving you are never sure if someone will ever look through the archive. That problem is there. Some major archives of mail-art are now in museums, but only researchers will go through them. They will hardly get to any public place where others can see it.