Form was working, but stopped emailing

I have two custom forms that are no longer sending emails:

Worked fine until a couple of weeks ago! I have changed nothing.
Created a separate test form and it works! It sends mail fine.
Joomla is set to use PHP Mail.
Checked events -> email -> general -> enabled is set to "yes."
Checked static -> to, subject, from are all filled in.
From is from the web site's domain name.

Any suggestions on where to start troubleshooting?

Hi bommerts,

Clearly something has changed so please check with your web host.

Please see this FAQ which may help.

Bob

I will open a ticket with my host but I want to make sure I narrow this down as much as possible.

I added a debugger onto the on submit event. It appears to be working, but no email is received:

Debug Data
email
1
Result
An email has been SENT successfully from user@domain.com to testuser@domain.com
Body
test email

Submitted by xx.xx.xx.xxx
Attachments
array ( )

Hi bommerts,

I'm not clear what you are asking?

You might try my Email [GH] action as that uses slightly different code to send the Email and has a better Error report than the standard action.

Bob

I wanted to know if there was anything further I could do to narrow this down. My fear was that my host would brush me off as a problem with my script (I've had this happen with previous hosts before)

I opened a ticket with them, however, and they have been very helpful. They found that my outbound mail was being blocked - looking into it now.

Thanks for your help.