domain name is reolaced with IP within email address

[offers]

Please, help!
when I am sending email out it comes back to root account and within the sender's email address instead of  my domain name it shows my IP address
(ex:   from offers@263.165.1.4    instead of     offers@advantage.com).
thnks

[aktiwari4u]

we need to see your configuration file to analyze the problem . it may be that you may have mentioned some wrong entry

[offers]

what configuration do you mean? the system, network or sendmail ?
another thing : the same email ( for the same user) address sometimes shows domain name but other times an IP ....it is unstable (btw, we are running linux on apple)
Thank you!...

[aktiwari4u]

i was asking for the sendmail configuration file . and i think you should also see the reverse dns entry for your system is proper or not in your dns server.