CMS Made Simple Forums

When I send a test email via the CMSMailer Test, its received just fine.

However when the contact form is submitted, a success message is displayed but the email is never received.

What do I need to check here please?

Makes no sense to me that the test passes but a real submission disappears into the void.

Check it is actually sent but never seen - spam folder?

Assuming you're using Form Builder, go to Extensions -> Form Builder -> Click form -> Send To -> "From address" for email: put and address using your domains as some hosts require this as a spam prevention.