ODMR

Mailkeep was the first public ODMR forwarding service on the Internet. That is our commitment to reliable and standard mail systems. ODMR allows users with dynamic IP addresses, NAT routers, firewalls and intermittent connections to receive SMTP mail. This option is even open to users behind ISPs that block all incoming connections.

On Demand Mail Relay (ODMR)

ODMR allows mail servers that cannot receive incoming connections to contact other mail servers (such as Mailkeep) and request mail delivery. The delivery takes place in the outgoing connection, which means it is not affected by Firewalls or access restrictions placed by ISPs.