Christopher J. Buckley

Whilst recently implementing DKIM and SPF for both my personal domain e-mail and for the corporate mail-servers I am responsible for, I found a great verification e-mail box from the DKIM mailing list.

If, after setting up your new extensions to the SMTP protocol, you wish to verify everything is working correctly then I thoroughly recommend a blank e-mail to this address: check-auth@verifier.port25.com

Let’s run through the results of this e-mail for my domain, cjbuckley.net:

 Summary of Results
SPF check:          pass
DomainKeys check:   neutral
DKIM check:         pass
Sender-ID check:    pass

Immediately, we can see that the implementations have been successful - this is a good sign!

SPF check details
Result:         pass
ID(s) verified: smtp.mail=example@cjbuckley.net
DNS record(s):
cjbuckley.net. 300 IN TXT "v=spf1 redirect=_spf.cjbuckley.net"
_spf.cjbuckley.net. 300 IN TXT "v=spf1 ip4:87.127.106.176/29 ip4:84.45.189.64/29 include:ukfsn.org -all"

The detail outputted from this SPF check is impressive; as we can see, my domain initially does a redirect to _spf.cjbuckley.net (note the underscore - these _are_ valid in TXT records). This allows many domains I am the hostmaster for (corporate ones, usually) to be easily managed.

For example, I use redirect: _spf.mycorporatedomain.com for all my corporate domains, this cleans up the SPF records and allows easy management of the record database - all other domains can be redirected to _spf.mycorporatedomain.com. It works very well, and is something I noticed Google taking advantage of, initially.. :-)

Next up - DomainKeys:

DomainKeys check details:
Result:         neutral (message not signed)
ID(s) verified: header.From=example@cjbuckley.net
DNS record(s):

The checker confirms that I do not have DK implemented - indeed, this is correct. DKIM replaces DK, and is now being driven forward to replace Yahoo! DomainKey’s. Note: gmail.com only verifies DK signatures, not DKIM yet - a bit disappointing, though they _do_ sign both with DKIM and DK.

 DKIM check details:
Result:         pass
ID(s) verified: header.From=example@cjbuckley.net
DNS record(s):
beta._domainkey.cjbuckley.net. 300 IN TXT "k=rsa; t=y;p=MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDiIfv9vqSRUo9L8
ztX/C4gfCD/Ivt8eAGyQbjJ2g4Rq764NPwauj5/sY2AfMrFPqhA0ieXWtmJy2gFS
c4ZlxT8KYaFsJATOpJfYAXUtzmmQ8+RcioyeN3LjzNhm1gUYyJI1Lw0yD2y+k
dN3YxY4NZ0esMXrKbsngTl3pNcNCNxXwIDAQAB"

We can see that our DKIM policy has been verified successfully. As dkim.org states:

DKIM lets an organization take responsibility for a message. The organization taking responsibility is a handler of the message, either as its originator or as an intermediary. Their reputation is the basis for evaluating whether to trust the message for delivery.

Given this statement, e-commerce, financial and banking organisations should have either implemented or be on their way to planning an implementation of DKIM. Personally, I find SPF flawed - DKIM is the wiser choice.

I’m hoping to blog a dkimproxy implementation guide shortly, as the published guide has a few advisories I have issue with and would like clarified.

Comments, welcome!