Sending bulkmail from different server?

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http://serverfault.com – I want to send bulk domains from my vps for a domain(cagetur.com) hosted in another company. The company(cagetur) will go on using the old hosting account for its mailing operations. The vps will just be used for smtp for once a week. I created an A record "vps.cagetur.com". directed it to the IP adress of vps then created a mx record with bigger preference number "50 vps.cagetur.com." on the domain control panel. When I trace the "vps.cagetur.com" i can reach my vps now. I installed hMail on the vps. Configure it (created domain, accounts). I have no information about "system" so i couldn' (HowTos)