Postfix authentication to ComCast port 587

[Michael ODonnell]

>  postfix/smtp[11991]: 3C4A1918124: to=<michael.odonnell at comcast.net>, relay=smtp.comcast.net[76.96.62.117]:587, delay=0.39, delays=0.01/0.02/0.33/0.04, dsn=5.1.0, status=bounced (host smtp.comcast.net[76.96.62.117] said: 550 5.1.0 <mod at e521> sender rejected : invalid sender domain (in reply to MAIL FROM command))
>
> ('e521' is not a valid domain name and not recognized by DNS.)
> I'm not sure where its getting e521 from, but you can probably
> change it using postfix - Unfortunately I don't remember the
> directive (or where to put the directive) to do that.  [...]
> Try giving it a domain name like c-99-99-99-999.hsd1.nh.comcast.net

Yup, that did it - I'm transmitting this message from the
machine in question rather than that icky WWW tool - many
thanks.  That error message about the Certificate on the line
just before it was apparently just intended to confuse me.

The setup scripts for the various MTAa have always used the
machine's hostname which, of course, is only known on my
little internal network and is not the hostname assigned to
my modem's WAN connection and from which the client appears
to be connecting.  In the past the ComCast SMTP server didn't
care how my clients ID's themselves but that's apparently
tightened up when using this "submission" protocol.

Dang.  This means it's going to be a PITA to keep my Postfix
config files up to date such that they stay in sync with that
externally visible hostname since it changes every time I get
renumbered.  I'll guess I'll have to do something scripty to
rewrite the config file and then restart Postfix every time
it happens.  >-/