Minimum delay between two user registrations with same IP

Hello folks,

I have a problem and I can't find any informations about it.

I want to create multiple accounts on my server and it doesn't work. (I tried with Adium and Pidgin) After creating an account I need to wait a while to create another one...or I need to change my IP to create immediately another one.

My configuration:
- in-band registration is enabled
- anonymous registration is disabled

I looked for a parameter like "min_delay_between_registration" or "max_registration_per_minute",... in documentation but I didn't find anything useful!

Any ideas?

Thank you :D