Which mailserver am i using?

[Xubuntu_user]

I have setup my computer with a mail server in RHEL to send and recieve mails. my mailsever is xubmail.com I have a dns solution to it for my dynamic IP. The first few mails that i sent were being sent from my domain like [email protected] then suddenly after some time my mails started going from some other domain the domain was [email protected] How did this happen? comcast is the ISP are all my mails going through their mail server? Can i change this thing so that mail could go from my domain only? Please help... I'm not too much into server configurations and might be possible that i have configured something wrong...

[Devasis]

Go to the mail that you sent from your domain and check its headers, you will be able to check from which mail server did the mail was sent. I think you have not congigured your mail server properly. Do you have DHCP configured by the ISP which gives you the IP and other TCP/IP configurations? May be that could be a problem. If your IP address is changing your mail server may be looking for a valid mail server and it reached your ISP's mail server...

[Xubuntu_user]

I too think its due to the DHCP IP addressing. Well but how can the mail go from my ISP's mail server? I don't know what else to do, i think i will have ti buy a static IP Address from my ISP. The mail sever was simple to use not much configurations were needed. May be that could be the problem too.. Will have a look and post back.. Thanks!
PS: I checked the headers and found that all mails were sent from th ISP's mail server...

[MrChris-]

Verify the MTA that was used to deliver the mail. See the mail log at the following location : /var/log/maillog. Here you will know which mail MTA used for delivering the mails...