Outgoing email problem

Hi – I have the GD Core Version 1.6.15, current add-ons, and WP 4.7. I have not been able to successfully send notifications to new users or receive admin notifications although I have been able to register new users and add listings.

When I started following steps from the forum to troubleshoot, the email address in the GD General > Email address was my GD username @ myserveraddress. I believe this address was the default when I installed GD.

I followed these steps from the forum:

1) Installed Email Log and invited some new members. The emails showed up in the log.
2) Installed SMTP Mailer to try to configure my server to send email from my site. I don’t really know the difference between PHP mail and SMTP but thought it was worth a try. I entered the settings from my server cPanel and think I did it correctly. Sent out test emails that showed up in the log and did not get error messages, but did not receive the emails at any of the email addresses that I used.
3) Spoke to my hosting provider to confirm I had the right SMTP settings and see what else my be an issue. They confirmed the SMTP settings and had me change my General setting email address to an address set up for my web site since there is not a way to check email associated with the original address I was using (gd username @ server address). They also had me change the MX Entry option so that the cPanel does not assume it is handling the email and will actually check the DNS settings. They also thought that sending email via PHP mail would work and that I should try that option again. So I am going to call them back to help me investigate the PHP mail option, but wanted to check in with you all first to find out how to get back to the proper defaults. So far, I have
4) Uninstalled SMTP Mailer and deleted associated data
5) Retested notifications (eg added some new users) still not working.

So my main questions are:
1) what should my General > Email address be? Is it supposed to be the default address at installation (at least I think it was the default) of GD username @ server address?
2) Any other settings I should confirm before talking to my hosting provider again about possible PHP mail troubleshooting?

Thank you