Should i use dkim

As the years wore on and the true complexity of the task became clear, the scope of what DKIM actually does narrowed considerably. Here's what it tries to do: To validate that the domain which purports to send the message actually sent it. That's it. This is information designed for back-end server processes, not end users. The message could easily be a phishing attack or contain a malicious attachment or have a malformed header designed to spoof the identity presented to the end users.

None of this is DKIM's problem. A message with no DKIM signature would seem to be one which is harder to assess by back-end analysis engines. Even by design, a single message which passes DKIM tests provides no useful information about the reputation of the sender or safety or accuracy of the message content.

Early on, some mail clients, especially web mail clients, displayed a little shield or something similar as a 'trust marker' when a message passed DKIM. The ones I've checked don't do that anymore, and for good reason: End users can't do anything with that information other than to make too much of it.

You might be thinking that DKIM sounds kind of useless, but perhaps we're just expecting too much of it. If we just lower our expectations and look on DKIM as a tool use by other back-end analysis engines to judge the reputation of sending domains, perhaps it could be useful.

If you look at a lot of email over time that DKIM has validated as coming from that domain, the idea is that you can be sure that it really is from that domain and judge the domain's reputation. This would be helpful input for an email analysis engine if you really could trust the domain authentication, but the replay attack above shows that you can't. They say to whitelist whole domains based on reputation and to judge whether a message has come from that domain based on DKIM.

Section 5. And this is what large sites are doing today: They are whitelisting certain other large sites which they decide are trusted and then letting messages pass through unscrutinized if they contain a valid DKIM signature from one of the whitelisted sites. This leaves open the possibility of retrospective analysis of those messages that might affect the domain's reputation, but it still doesn't make sense.

With the replay attack, the domain specified in the DKIM signature is an innocent bystander, and there's no sense in diminishing its reputation. Trend Micro is a major provider of email security services and they say they are seeing messages performing exactly this sort of abuse out in the wild.

Even if DKIM performed as advertised, with the modest claim of sender domain authentication, I'd have to call it disappointing and of speculative value.

But it doesn't perform as advertised, and when administrators follow the guidance in the Development, Deployment and Operations document it can be far worse than disappointing. Clearly the problems which cause DKIM to be unreliable aren't addressed in any Internet standard and they probably can't be.

Only proprietary implementations of email security products can look for things like double From: headers. Standards, and especially sender authentication standards, have failed us. Security company faces backlash for waiting 12 months to disclose Palo Alto 0-day. RHEL 8. CISA warns of equipment vulnerabilities from multiple vendors. Costco customers complain of fraudulent charges before company confirms card skimming attack. Once the signature has been validated, the recipient server tries to retrieve the public key for the sending domain.

The public key decrypts the encrypted hash sent. The receiving mail server then computes its own hash. If the two matches, the message is let through. DKIM alone does not prevent domain spoofing. The best way to manage this is by adding your new keys, and a few days later removing your old keys DNS records for your domain.

Postmark is one of the only ESPs that make it easy to manage this rotation because we keep your old private key active while your new public key propagates. Don't miss our other guides on these protocols to learn more about how they work together to protect your domain. Yes, and no.

Zachary Harris found a vulnerability in short DKIM keys that allowed him to factor bit keys in about 24 hours. This tells the receiving mail server which DKIM key should be used for validation.

Our premium DMARC monitoring with a single dashboard to monitor all mail sources, 60 days of history, and actionable recommendations. Our monthly newsletter is packed full of email tips, product announcements, and interviews with industry experts. DKIM lets you add a digital signature to outbound email messages in the message header.

When you configure DKIM, you authorize your domain to associate, or sign, its name to an email message using cryptographic authentication. Email systems that get email from your domain can use this digital signature to help verify whether incoming email is legitimate. In basic, a private key encrypts the header in a domain's outgoing email.

The public key is published in the domain's DNS records, and receiving servers can use that key to decode the signature. DKIM verification helps the receiving servers confirm the mail is really coming from your domain and not someone spoofing your domain.

You can choose to do nothing about DKIM for your custom domain too. If you don't set up DKIM for your custom domain, Microsoft creates a private and public key pair, enables DKIM signing, and then configures the Microsoft default policy for your custom domain.

Microsoft's built-in DKIM configuration is sufficient coverage for most customers. However, you should manually configure DKIM for your custom domain in the following circumstances:. When you forward a message, portions of that message's envelope can be stripped away by the forwarding server.

Since the digital signature stays with the email message because it's part of the email header, DKIM works even when a message has been forwarded as shown in the following example. In this example, if you had only published an SPF TXT record for your domain, the recipient's mail server could have marked your email as spam and generated a false positive result.

The addition of DKIM in this scenario reduces false positive spam reporting. DKIM uses a private key to insert an encrypted signature into the message headers. If the message is verified, the DKIM check passes. If you do not see it, add your accepted domain from domains page. Once your domain is added, follow the steps as shown below to configure DKIM.

Make sure that the fields are set to the following values for each:. Microsoft automatically sets up DKIM for onmicrosoft. No steps are needed to use DKIM for any initial domain names like litware.

Since both and bitness are supported for DKIM keys, these directions will tell you how to upgrade your bit key to in Exchange Online PowerShell. The steps below are for two use-cases, please choose the one that best fits your configuration.

When you already have DKIM configured , you rotate bitness by running the following command:. Stay connected to Exchange Online PowerShell to verify the configuration by running the following command:. This new bit key takes effect on the RotateOnDate, and will send emails with the bit key in the interim. After four days, you can test again with the bit key that is, once the rotation takes effect to the second selector. If you want to rotate to the second selector, after four days and confirming that bitness is in use, manually rotate the second selector key by using the appropriate cmdlet listed above.

If you haven't read the full article, you may have missed this time-saving PowerShell connection information: Connect to Exchange Online PowerShell. If you have provisioned custom domains in addition to the initial domain in Microsoft , you must publish two CNAME records for each additional domain. Instead of looking up the MX record for your initialDomain to calculate domainGuid , instead we calculate it directly from the customized domain.

For example, if your customized domain is "contoso.