Jay, I'm not speaking for Spamhaus or 1&1 here, but some hosting providers
do outbound spam detection, and treat outbound mail that they believe is
spammy in a different way than their customers' less suspicious outbound
mail. In 1&1's case, it appears that they route the suspicious outbound
mail via IPs that they've reserved for this purpose. Receivers can then set
up a policy for how to treat that suspicious mail. I presume 1&1 asked
Spamhaus to list those special-purpose outbound IPs as a courtesy.

Microsoft Office 365 takes a similar approach and tags suspicious outbound
messages with a header that identifies them as suspect.

Paul Kincaid-Smith

On Wed, Feb 14, 2018 at 11:12 AM, Jay Hennigan <mailop-l...@keycodes.com>

> On 2/14/18 9:47 AM, Paul Kincaid-Smith wrote:
>> Hi Scott,
>> Spamhaus lists that IP as a "courtesy SBL listing" -- presumably at the
>> request of the IP's owner. Here are other IPs Spamhaus lists as a courtesy:
>> https://www.spamhaus.org/sbl/listings/courtesy.spamhaus.org
> So how exactly does that work? The address holder contacts Spamhaus and
> says something like, "Hello, Spamhaus. I'm a notorious and deliberate
> spammer and plan on sending several metric tons of spam from the following
> IPs. Could you please list these IPs as a courtesy to my potential victims?
> OK thanks, bye" and then they do so?
> --
> Jay Hennigan - CCIE #7880 - Network Engineering - j...@impulse.net
> Impulse Advanced Communications  -  http://www.impulse.net/
> Your local telephone and internet company - 805 884-6323 - WB6RDV
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