Microsoft O365 labels nanog potential fraud?

William Herrin bill at
Wed Mar 29 15:12:33 UTC 2017

On Wed, Mar 29, 2017 at 3:04 AM, DaKnOb <daknob.mac at> wrote:

> Usually mailing lists act like e-mail spoofers as far as SPF and DKIM is
> concerned. These two systems above try to minimize spoofed e-mail by doing
> the following:
> SPF: Each domain adds a list of IP Addresses that are allowed to send
> e-mail on their behalf.
> DKIM: Each email sent by an "original" mail server is cryptographically
> signed with a key available, again, in the DNS.
> When you send an e-mail to a list, you send it to the mailing list mail
> server. After that, of the server forwards that e-mail to the recipients,
> its original address is shown, therefore if Outlook checks for SPF records,
> that check will fail. An easy way to get around this is for the list to
> change the From field to something else, like "Mel Beckman via NANOG" and a
> local email address.
> However, when you send that email, it may also be signed with DKIM: any
> change in subject (say "[NANOG]" is added) or the body (say "You received
> this email because you subscribed to NANOG" is appended) will also cause
> that check to fail.


Both SPF and DKIM are meant to be checked against the domain in the
envelope sender (SMTP protocol-level return address) which the NANOG list
sets to nanog-bounces at Checking against the message header "from"
address is an incorrect implementation which will break essentially all
mailing lists.

Bill Herrin

William Herrin ................ herrin at  bill at
Dirtside Systems ......... Web: <>

More information about the NANOG mailing list