When we set inkscape-devel@ up, we set it to post-by-anyone to make it easy for people not subscribed to be able to send emails.
However, in recent weeks we seem to be receiving an unusually high amount of spam.
A few months ago the inkscape-user@ list was suffering the same situation, and reached a concensus to have list posting closed to non-members. This resulted in immediately preventing the spam emails. It also had the predicted downside of preventing some people from posting to the list, but so far this has been a fairly low level problem (most of the complaints were from people who didn't have much experience with mailing lists in general, and could be addressed with a little education).
Like many on this list, I've always been in the camp of keeping list posting open to non-members, however, given inkscape-user's success, it might be worth considering.
What do others think?
Bryce