[Mailman-Users] Mails not writing to archive immediately

I've just been mailed by one of my users to say that the archive for my list is not up to date. Having just checked prior to sending this, I found that by clicking on the "Date" link for this month, the last message written to it is nearly a week old. Downloading the Gzip'd text file (which never actually shows the correct size - any ideas?) brings me forward to only approximately 24 hours behind.

Does anybody know why this is - I'm assuming messages that get posted to the list should also hit the archive at the same time.

Rgds

MD