IRC oftentimes masks the direct IP or sometimes will only give you the hostname. If you don't see it in the docs, try converting to the IP address with
Net::DNS::Resolver. It looks like the Net::IRC::Event object has a host() that returns (or sets) the hostname for each item that you get. That should work fine.
Also event 307 is marked as 'userip' and is listed as an "Undernet extension". You might want to look at that. Cheers.
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jb