I am experiencing some weird bugs over the past day or so. Basically we are using Zoo Visitor to allow some of our team to create users without having access to the Members section of the CP, for obvious security reasons, but each time they create a new account over the past day or so, this error is being thrown:
ExpressionEngine - An unknown error has occurred when sending email with your server.
This same error comes up when trying to update a user's member group. I've run a few searches and I can't find anything that has changed over the past day, but if I knew what caused this error it may be easier to debug properly.