The install script, as I've been discussing here, isn't all that well behaved in situations where the mail server lives behind a NAT box.
I'd like to propose how it ought to work, for comment, and if everyone agrees, then someone can patch the script.
Currently, the script appears to assume that the FQDN that the machine knows itself by is the domain name for which it will process mail, and that's almost never correct.
It's *often* correct to lop off the first element, and assume that.
That adjustment made, the install script should probably ask if it's assumption about the domain is correct (it might not be: franklink.corp.example.com might be the mail server for example.com), and once it's got the right idea, *then* is should check to see that a) it can find an MX record for that domain and b) that MX record points back to it's local interface IP.
In the long run, it would be nice to figure out why the mail server *needs* an MX record for the domain... but I suspect that's postfix-expert territory.
Anybody know any reasons why this would not be a suitable modification to the installer?