TOL publishes a list of their mailservers and also has them listed at DNSWL.

The list auf these ~20 IPs probably is in many configs somewhere. And/or a 
DNSWL query.
F.e. when TOL gets listed on Spamcop or others again.


-----Urspr√ľngliche Nachricht-----
Von: <> Im 
Auftrag von Henry R
Gesendet: Samstag, 10. Dezember 2022 04:47
Betreff: google's receiving policies

t-online has no SPF & DMARC & DKIM settings. but google try to maintain a 
reliable sender IP list for them.

if you forward a message which is original from t-online to gmail, if you don't 
have SRS enabled for this forwarding, gmail will just reject it.

as far as I know, many ISP level forwardings have NO SRS setup, including,, and even Outlook.

since there is no spf, no dkim for t-online, how google know it's coming from a 
valid IP? the only reason I can image is that google help maintain that a ip 
list for t-online itself.

how do you think of this?

Thanks & regards.

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