SPF and domain keys

Mike Ragusa mragusa at gmail.com
Mon Aug 29 15:00:49 UTC 2016 

Yes of course as that would be the original sender of the email and their
information would also be in your SPF policy. You can change the Sender and
Reply-to headers to be from your domain and mask it a bit better but the
 received by headers would show the alphazulu.com mail server.

On Mon, Aug 29, 2016 at 10:38 AM project722 <project722 at gmail.com> wrote:

> Awesome, Actually one more question. If we allow folks from another domain
> to send as us is there a chance anywhere in any of the email "from" headers
> it would reveal the "true" domian?
>
> eg..
>
> folks at alphazulu send as @foxtrot.com.
>
> Would @alphazulu.com appear anywhere in the headers?
>
> On Mon, Aug 29, 2016 at 9:34 AM, Mike Ragusa <mragusa at gmail.com> wrote:
>
>> Glad to help! If you need a low cost DMARC reporting service, I would
>> recommend www.dmarcian.com
>>
>> On Mon, Aug 29, 2016 at 10:33 AM project722 <project722 at gmail.com> wrote:
>>
>>> Thanks guys - very helpful information indeed.
>>>
>>> On Mon, Aug 29, 2016 at 9:08 AM, Mike Ragusa <mragusa at gmail.com> wrote:
>>>
>>>> Ideally it is best to use both technologies and then put DMARC on top
>>>> to ensure reporting and enforcement of the policies. DKIM cryptographically
>>>> signs your messages and SPF informs receiving mail servers of who is
>>>> allowed to send on your behalf.  You should not think of using only one or
>>>> the other as they work best together to accomplish the same goal. When
>>>> utilizing DMARC on top of it all, you get the added benefit of reporting
>>>> from over 200 different ISPs from around the world. In general, DKIM is
>>>> first used as the authentication method and SPF as a backup.
>>>>
>>>> If you have a valid DKIM key, then failed SPF should not matter but if
>>>> you have a failed DKIM key and SPF passes, there still may be
>>>> deliverability issues to account for. If you do enable DMARC, then your
>>>> DKIM and/or SPF headers must align with your domain or you will encounter
>>>> deliverability issues depending on how your policies are setup. DKIM in
>>>> relaxed mode allows for mail to pass the test with the same parent domain
>>>> but canonicalization requires that your domains match up exactly as stated
>>>> ie example.com and mail.example.com are not the same and will fail.
>>>> SPF with DMARC requires two or more FROM headers (
>>>> https://tools.ietf.org/html/rfc2822#section-3.6.2) match up exactly or
>>>> it will fail SPF checks but without DMARC anyone listed in the sender
>>>> policy can send on your behalf. While this may seem strange at first, this
>>>> is to prevent people from signing up to something like google and sending
>>>> on your behalf with the default google DKIM key and a wide open SPF policy.
>>>>
>>>> With DMARC:
>>>> DKIM : headers must match domain or else fail
>>>> SPF:  2 or more headers must match domain or else fail
>>>>
>>>> Without DMARC:
>>>> DKIM: just needs to be signed by sending mail server
>>>> SPF: just needs to be send from a valid sender
>>>>
>>>> Depending on your needs, I would recommend putting SPF in soft fail,
>>>> DKIM in relaxed mode and DMARC in reporting mode only for the first 15-30
>>>> days and see how your traffic looks and who is sending on your behalf. Once
>>>> you have a comfortable baseline, start to tighten up your policies.
>>>>
>>>>
>>>>
>>>>
>>>> On Mon, Aug 29, 2016 at 9:51 AM project722 <project722 at gmail.com>
>>>> wrote:
>>>>
>>>>> What about DKIM only? Can it be used instead of, or, as a
>>>>> "replacement" for SPF? For example mails are signed with DKIM from the SMTP
>>>>> servers, and the receiving servers are checking both SPF and DKIM. If the
>>>>> receiving server detected a missing SPF would it allow mail through if DKIM
>>>>> is present and valid? I suppose a lot of this depends on the SPF policies
>>>>> enforced on the receiving side.
>>>>>
>>>>> On Mon, Aug 29, 2016 at 1:53 AM, Dave Warren <davew at hireahit.com>
>>>>> wrote:
>>>>>
>>>>>> The easiest answer is: Whatever you want. Strictly speaking,
>>>>>> alphazulu.com can send mail on behalf of foxtrot.com using a
>>>>>> alphazulu.com DKIM selector, and that's perfectly valid under DKIM.
>>>>>> However, it won't have DMARC alignment, which is becoming more and more
>>>>>> important, so if alignment is relevant, you'll need to use a
>>>>>> foxtrot.com selector.
>>>>>>
>>>>>> tl;dr: Use a foxtrot.com selector unless you simply can't.
>>>>>>
>>>>>> As for who generates it, it's irrelevant. The sending server will
>>>>>> need the private key, your DNS records will contain the public key, but it
>>>>>> makes no difference if foxtrot.com creates the keys and delivers
>>>>>> them to the appropriate parties, or if alphazulu.com generates
>>>>>> generates a private key and provides the alphazulu._
>>>>>> domainkey.foxtrot.com record to foxtrot.com.
>>>>>>
>>>>>> Remember that you can have as many selectors as you want, don't reuse
>>>>>> them across trust boundaries (in other words, consider that in the future,
>>>>>> foxtrot.com and alphazulu.com may part ways, when that happens, it's
>>>>>> ideal if you can remove the selector from your DNS (after a period of time,
>>>>>> at least a week), such that alphazulu.com cannot continue to sign
>>>>>> mail. It's also ideal if you don't have to update DKIM records elsewhere in
>>>>>> your infrastructure.
>>>>>>
>>>>>> I hope at least some of this makes sense, but if not, ask. DKIM and
>>>>>> DMARC are fiddly, and a lot of the DKIM advice out there isn't entirely
>>>>>> complete now that DMARC is on the scene and DMARC builds on top of DKIM and
>>>>>> SPF.
>>>>>>
>>>>>>
>>>>>> On Sun, Aug 28, 2016, at 16:13, project722 wrote:
>>>>>>
>>>>>> Lets say my domain is foxtrot.com and we have SPF records for the
>>>>>> SMTP servers on foxtrot.com. Now lets say I have decided I want to
>>>>>> allow alphazulu.com to send mail as foxtrot.I know how to add
>>>>>> alphazulu.com to the SPF but If I wanted to also use DomainKeys or
>>>>>> DKIM to authenticate alphazulu.com would the keys need to be in
>>>>>> foxtrots name or alphazulu? For example,
>>>>>> Would I use:
>>>>>>
>>>>>> _domainkey.foxtrot.com.                  IN TXT          "t=y\;
>>>>>> o=~\;"
>>>>>> xxxxxxx._domainkey.foxtrot.com.           IN TXT          "k=rsa\;
>>>>>> p=xxxxxxxxxxx
>>>>>>
>>>>>> or
>>>>>>
>>>>>> _domainkey.alphazulu.com.                  IN TXT          "t=y\;
>>>>>> o=~\;"
>>>>>> xxxxxxx._domainkey.alphazulu.com.           IN TXT          "k=rsa\;
>>>>>> p=xxxxxxxxxxx
>>>>>>
>>>>>> Also,
>>>>>> 1) Who generates the keys? Foxtrot or Alphazulu?
>>>>>> 2) Would I need both SPF and keys or would keys alone be enough to
>>>>>> authenticate the other domain? ( I am in a position where I would like to
>>>>>> use only keys)
>>>>>> 3) Which one is better to use in terms of provider checking? For
>>>>>> example, are providers even checking keys as much as they are SPF?
>>>>>>
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>>>>>
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>
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