[CentOS] Sendmail failing on home machine

[John R Pierce]

Peter Loron wrote:
> I have a CentOS 5 machine at home, behind a NAT gateway. Among other 
> things, I'm running mdadm in monitor mode to alert me to RAID 
> failures. I want it to send messages to my main email address. Any 
> messages I send from the home CentOS box to that email address are 
> being rejected with this error:
>
> Deferred: 451 Could not complete sender verify callout
>
> My understanding is that the destination mail server is trying to 
> connect back to the source email host via SMTP as an anti-spam check 
> and is failing.
>
> My external IP is set up with a dynamic DNS entry, so I guess I could 
> set up an MX record and actually receive mail on the home box, but I 
> don't want to deal with the security issues or the spam.
>
> Any suggestions for allowing sendmail-dependent apps running on the 
> home machine to be able to send mail?

configure your sendmail to use your ISP's mail server as a 'smarthost'.