I have Opt-in mail 4.00 and for some reason it has stopped sending mails out altogether. I have cleaned up the subscriber list and still it does not work.
This has been the case since December (19 December was the last successful mailshot) but I have not posted here because I think that I have missed something simple.
Problem solved - one admin changed the distribution rights to the e-mail list and didn't tell anybody. Doh!