[Exim] Some research

Hi,

i'm doing some research on the topic "who uses exim".
For this i filtered my imap mailbox for the Received lines, and looked
for messages with exim-like IDs in it (matching \w{6}-\w{6}-\w{2}).
The results so far are interesting, my question now is, does any other
mail-software uses ids like this?

ciao