Re: Federated, decentralised communication on the internet (was: domain names, was: hostname)
On Wed, Mar 21, 2018 at 02:53:47PM -0500, David Wright wrote:
> HELO dotlessdomainname
> HELO dotcontaining.home
> I want someone to explain to me why having a dot is better then not
> having a dot in deciding whether a submitter is genuine. And
> without the politics.
My understanding: the SMTP receiver will use whatever heuristics it
finds appropriate to avoid receiving spam.
One heuristic that is commonly used is to reject all messages where
the HELO doesn't even syntactically qualify as a valid FQDN -- in other
words, has no dot in it.
Another heuristic that is commonly used is to perform a DNS query on
the HELO string, and reject it if it's not a valid FQDN based on DNS.
The first heuristic is much less expensive to perform, as it does not
involve sending a DNS query and waiting for the response. The test
is simply a syntactic scan of the input string that it already has.
Of course, a given receiver may choose to perform BOTH tests.
For the person who is trying to send legitimate outgoing mail, obviously
you don't want your messages to be rejected as spam. So it behooves you
to make sure your message complies with not only the applicable standards
(SMTP = RFC 2821, etc.), but also with the known practices of potential
receivers. Which means, among other things, having a HELO string that
won't cause your message to be dropped as probable spam.