Re: reject_unknown_hostname either/or

On Tue, 15 Jun 2004, Dave wrote:

> >From the postfix docs:
>
> reject_unknown_hostname
> Reject the request when the HELO or EHLO hostname has no DNS A or MX
> record.
>
> I'm having a little debate with a co-worker on the interpretation of "has no
> DNS A or MX record". He says the quantative "or" means the domain must have
> both an A and MX record or the mail gets rejected
>
> My interpretation was that the "or" means any one of type A or MX will allow
> a pass, but if both are missing the mail is rejected.

You are correct, since 'or' does not mean 'and'. The code is in
src/smtpd/smtpd_check.c, see reject_unknown_hostname there; not much to
it. What's more important here is whether or not the level of false
positives inherent with reject_unknown_hostname is acceptable for your
organization or not; many otherwise legitimate clients still HELO with
hostnames that are (at least externally) not resolvable.

-Rob