I run a multi-site blog with about 300 sites.
I have an idea that I want to write a plugin that in order to add all administrators of blogs to a MailMan mail-list. I just want administrators though, I don't want to add editors and subscribers to this email list.
I want to capture the event of being assigned an administrator of a blog. Then I'll send an email to the subscribe email address of my mail list to automatically add the person.
So I was wondering which hook should I use ? I think I want to send an email every time a person is set as an administrator. I don't care if they are removed as an administrator.