Site email broke by host; fixed; now only half working: WTF?

Hello

Email contact was broke for my site -

http://cohousing.org.uk

The host had reset the email server address - that's now been fixed. I know this because the website is now sending me new registrations again.

But the contact forms still don't work. I've tried sending to several emails, using the site-wide contact form as well as personal ones. None are getting through. No warning from the site - I get the "mail sent" banner.

Anyone got any ideas? I'd write to the host again - but if new registration alerts are coming through, it wouldn't appear to be their bad.

Cheers,

Dan