The reason is sounds technical is probably that it is rather technical... ;)
It's perhaps best to take it step by step.
Transferring email on the Internet requires port 25. So the first thing to do is to make sure that the device you use to connect to the Internet (DSL modem, router or whatever) has port 25 open, and that any incoming traffic on port 25 is redirected from there to port 25 on the server running Mercury. Make sure there is no firewall program on the Mercury server that blocks port 25.
To send an email you set the SMTP server in your email program to the IP address of the Mercury server. If you run the email client on the same computer as Mercury you should set it to localhost or 127.0.0.1 (which is the same thing). Your email is then received by the SMTP server module in Mercury, and sent to non-local recipients via the SMTP client module (either MercuryE or MercuryC).
To receive an email from someone via the Internet you need to make the public IP address for the mail server handling your domain known to the world. To do this you add a MX record to the DNS information for your domain, containing the hostname of the server. This could be mail.myownserver.info. You will then need an additional A record that gives the IP address for that hostname (which you have, IP is 76.125.92.139).
The MX records for myownserver.info now point to mail6.zoneedit.com and mail7.zoneedit.com, which presumably is not what you want, so you need to change that.
I'm not able to connect to port 25 on 76.125.92.139 at present, so that's another thing you need to check on.
/Rolf