Site email notifications not working correctly. Please help.

Hi guys,

For some reason our site email notifications don't seem to be working and I can't quite figure out why, the standard email settings and address are all correct on the site.

I was wondering if it may be a plugin causing it but I'm not sure how to find that out.

The new user notifications don't work and neither do emails from the quiz plugins we have.

Any pointers would be very helpful. Or plugins that could help us solve the issue.

Many thanks