1) Create 2 DNS records at your DNS servers:
An A record:
mail.yynot.tzo.com at your public IP
and:
MX record with a weight of 10 for mail.yynot.tzo.com
2)Create a domain on the SME of yynot.tzo.com (unless that is the domain name of the server itself).
Now email requests will look up the MX record, find the A record and relate it to your IP address and the SME will accept it if it has a domain matching it.