The End-To-End Internet (was Re: Blocking MX query)

Sean Harlow sean at
Thu Sep 6 00:37:46 UTC 2012

On Sep 5, 2012, at 19:07, John Levine wrote:

> Not really.  Large mail system like Gmail and Yahoo have a pretty good
> map of the IPv4 address space.  If you're sending from a residential
> DSL or cable modem range, they'll likely reject any mail you send
> directly no matter what you do.

While I've clearly been on the side of "don't expect this to work", "why do you have your laptop set up like that?", and defending the default-blocking behavior on outbound, this is not true at least for Gmail.  I have a test Asterisk box which I've been really lazy about setting up properly that successfully sends status messages from my home cable modem to my Gmail-hosted personal domain every day, even getting through with a completely bogus source address.  It's never even been flagged as possible spam.

Maybe Gmail does more detailed analysis of some kind and sees that I'm also checking my email from the same IP that's sending these messages, I don't know, but they are not just blocking anything coming in from a random cable IP.  I'll bet it raises the "spam likelihood" or whatever as it probably should, but it's not a total block.
Sean Harlow
sean at

More information about the NANOG mailing list