issue with sending emails from Wordpress

Hello:

I have an issue that my site is not sending notification emails to us.

We use ninja forms and WP Mail SMTP to send the submissions to us, the submissions are on the site but we never got it. This happens since yesterday.

I need this to be fixed today!

We have 2 sites one is a subdomain but independent, that subdomain is really slow. You should find why and fix it.

I know this will take only some hours for the candidate who knows who to do it so bid accordingly.

And more this is going to be also a test project to find a freelancer I can count on for future work.

thanks