| [reply] [Watch: Dir/Any] |
If you don't want to hardcode it, make it configurable for your users. You can also look up the MX record of the domain of the intended recipient and deliver the mail there. But delivering mail is a harder problem than you might think, because of Greylisting and firewalls and other stuff. So I think it's best to leave that up to the user.
| [reply] [Watch: Dir/Any] |
Perhaps you could set the default value of your configurable option to the MX record of the sender address. That should work fine in many cases, I guess.
| [reply] [Watch: Dir/Any] |