I'm looking for a method or something that can enable me to execute some code when a user is added or modified. Is there such a thing in Kentico 4? If not, is there any other way to do it?

I have to synchronise with a mailing client every time a user is added or modified in the database by calling a method called "SynchUser" which will update or create that user in a mailing client using their API.

We had something which was working until recently, but I can't find what. I now have to replace it somehow.

Thanks for any help.

Nathalie