Sorbs decided to list 188.8.131.52 which is the IP that the cpan.org mail goes through.
I'm not entirely sure why (a bounce? evil user?, ...) but they are making it a pain to get de-listed and I just lost patience navigating their slow, broken-link-ish, wordy website. So, if you or your ISP blocks mail based on SORBS you might miss your cpan.org (and other perl.org) mail. Too bad for you.
(On a similar note: If you or your ISP are using Spamcop you'll every few months lose some perl.org list mail because some idiotic spamcop user/perl.org subscriber submits a mailing list mail to that system).
Update: Robert just told me we had trouble with our virus scanner (it wasn't updating the definitions) so for a few days we were bouncing some new viruses instead of just dropping them in a giant file never to be looked at like we usually do. Their "spamtrap" was joe-jobbed and we bounced a mail to it. Anyway, if you know anyone at SORBS feel free to make them de-list us. Thanks.