When I change my domain, emails stop working

I have a site hosted with GoDaddy (my first problem I know!) and when I was setting it up I was using the temporary domain

https://266.443.myftpupload.com

Everything works fine, and if someone fills out a contact7 form (or a jetpack contact form) I receive the email no problem.

So then I changed the domain to about.thefeedbackclub.com – a subdomain of https://www.thefeedbackclub.com

The switchover works fine, and I can see that all the links in the site are updated to about.thefeedbackclub.com but all email notifications from Contact7 stop. If I switch back they work, if i use about….. they stop.

I have tried everything I can think of including:

1. Building a new form so it is picking up the new credentials
2 Trying to use SMTP Postman and connect to gmail via the api (apparently GoDaddy blocks this)
3. Manually changing the From addresses in the contact7 forms to any variation I can think of
4. Trying to continue to send as [email protected]
5. Swearing at my computer

i have another site https://www.tattsamistake.com running on godaddy that works perfectly with its own domain. The only differences I can see between the 2 set-ups is:

1. For about.thefeedbackclub.com I am using a subdomain
2. If I look in the settings for about.thefeedbackclub.com in godaddy it says the A record needs to be set up (even tho it is). I am hesitant to leave this overnight to resolve (if it does) because all my forms stop working. Although if waiting for this to resolve would help I of course would
3. The tattsamistake DNS settings has a CNAME record of email – email.secureserver.net (or very similar) which my about.feedbackclub.com doesn’t – although I added it but it didn’t make any difference

I don’t know whether my problem is:

1. I should just wait 48 hours and everything will miraculously start working again once all the DNS records are resolved
2. It doesn’t like the fact that it is using a subdomain – the actual domain uses gmail, but then again so does tatts a mistake and it works fine
3. The wordpress install has ‘hard-coded’ the ‘266.443.myftpupload.com’ settings and won’t change them over when I update

So I would really, really appreciate help in achieving one of the following outcomes:

1. Sending emails when I am using the about.thefeedbackclub.com domain. Right now they are just notifications to me – so any old hack to make that occur would be fine in the short-term

2. Keep the ‘266.443.myftpupload.com domain and someone use an alias or ‘something’ so that if someone types in about.thefeedbackclub.com it resolves to the site BUT when I click on the links it keeps that URL (right now I can type in about.thefeedbackclub.com and I appear at the site and it keeps that URL in the browser window, but as soon as I click on any link it reverts to 266.443 etc etc et

Help please!!!!