By way of explanation (because some list members asked me earlier), the
list host (MailmanLists -- thanks for the hosting!) had suspended the
zeromq-dev list for a few days due to it being the target of a large
spam run. They've now been able to apply some more targeted spam
protection, and re-enable the zeromq-dev list.
I think any messages sent to zeromq-dev in the last few days will
probably have bounced back, and so if there's anything important you'll
want to re-send it.
Ewen