Campaign slots and priority slots

Two limits, and they are easy to mix up.

Campaign slots — how many campaigns you can run at the same time. Every account has three.

Priority slots — how many of those can jump the queue. A new account has none.

Only a campaign that is still running holds a slot. Finish one and the slot is free again. Priority is not tied to the campaign you first spent it on either — switch it off one and on to another whenever you like.

A membership raises both, or you can buy slots on their own without one.

Priority is one of only two things that genuinely changes delivery speed, and you can see what it is currently worth on completion times.