channel mode +j (join throttle)

[slingamn]

https://freenode.net/kb/answer/channelmodes

This mode takes one parameter of the form n:t, where n and t are positive integers. Only n users may join in each period of t seconds, so with e.g. 3:10 only 3 users could join within 10 seconds. Invited users can join regardless of +j, but are counted as normal. You can use this mode to prevent bot attacks. Observe the average join rate of your channel and pick a good value for +j. This mode could be combined with +f to forward throttled users to an overflow channel.

[slingamn]

This seems largely redundant with #1509