> That's answers the second part of the question I initially asked,
> where the reverse and forward domains don't exactly match for any of
> the reasons you mention below.
> What I am not sure about is who's problem is that? Is it mine on the
> receiving end, or theirs? If they are using mismatched hosts is that
> not something they are doing in a non standard way, and if so why
> should I open myself up to more spam to accommodate them?
> I'm not exactly a networking person so I don't know, just asking to
> learn..

 The simple answer is that it's your problem. There is no requirement
for a sending server to have either reverse DNS for their IP address
or an IP address that correlates to either the MAIL FROM domain/host
or the EHLO name that they use.

 Note that there are two sorts of requirements in SMTP in general. One
sort is merely written down in RFCs as a 'MUST' (not a 'SHOULD', that's
just advice), but in practice nothing fails to work if someone violates
it. The other sort is a practical one required for SMTP email to work,
either based on the RFCs or just based on what large, influential hosts
require in order to talk to you. Today, for example, a resolvable MAIL
FROM host/domain is a practical requirement in that if you try to send
email without it, the majority of mail servers will not accept your

 There are some (or many) 'requirements' that are merely RFC
requirements, not practical ones. Unsurprisingly you will find many
perfectly good mail senders out there on the Internet violating these
RFC requirements, because nothing important actually enforces them
and so forces these sending hosts to pay attention. You can insist on
holding sending hosts to the letter of RFC requirements, but you should
not be surprised to find hosts violating them that send you legitimate
email and when this happens, the sending host may have absolutely no
interest in changing things to accomodate your strictness. (They may not
even notice.)

        - cks

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