Exchange Server 2003 is a common Windows email server. DKIM is a method for associating a domain name to an email message, thereby allowing email sender claims some responsibility for the email. In this topic, I will introduce how to add DKIM signature to outgoing emails in Exchange Server 2003. This tutorial is also suitable for Exchange Server 2000. I will also introduce DKIM selector and sender rule usage.

How DKIM works?

DKIM combines of a public key cryptography and a DNS to provide credible domain-level authentication for email.

When an email claims to originate from a certain domain, DKIM provides a mechanism by which the recipient system can credibly determine that the email did in fact originate from a person or system authorized to send email for that domain.

Therefore, to sign an email with DKIM in Exchange Server, you MUST have a private key/public key pair for email signing. The work flow is illustrated as follows:



Because DKIM signer uses private key to sign the email, recipient system uses public key to verify the signature, therefore, if signer doesn't expose the private key to third-party, the DKIM signature cannot be faked.

Here is a fast HTML version for this topic:
https://www.emailarchite.../dkim_exchange_2003.aspx

Edited by user Thursday, January 12, 2017 8:50:39 PM(UTC)  | Reason: Not specified

Create DKIM for Domain

Click "Domainkeys/DKIM" in Manager and click "New" to create a new domain DKIM signature. DKIM signature is based on the domain of sender email address. It is nothing about the Exchange server name. For example, if you want to sign the email from *@emailarchitect.net, please input emailarchitect.net to Sender Domain.

Certificate for Key Pair

You don’t have to use certificate issued by third-party authorities, I strongly recommend that you use DKIM manager to generate certificate automatically.​​​​​​​​​​​​​​



You can simply input your sender domain, use default settings for other parameters, finally click "Save" to create your DKIM signature.

Here is the detailed information about DKIM parameters:

DomainKeys/DKIM Parameters:

Sender Domain:
DomainKeys/DKIM signature is based on the domain of sender email address. It is nothing about your server name. For example, if you want to sign the email from *@emailarchitect.net, please input emailarchitect.net to Sender Domain.

Selector:
To support multiple concurrent public keys per sending domain, the DNS namespace is further subdivided with "selectors". Selectors are arbitrary names below the "_domainkey." namespace. To learn more detail, please refer to Selector section. For a new domain, you can simply use the default value "s1024".

Active:
If you have this option unchecked, DomainKeys/DKIM for this domain will be disabled.

Signature:
Default value is: Both DKIM and DomainKeys. You can also choose "DKIM Only" or "DomainKeys Only". We strongly recommend that you select "Both DKIM and DomainKeys".

Canonicalization Algorithm:
nofws/relaxed is recommended and it has better compatibility.

DKIM Signature Algorithm:
On Windows 2000/2003/XP, rsa-sha1 is the only option. On windows vista/7/2008 or later version, you can choose "rsa-sha1" or "rsa-sha256". "rsa-sha1" gives better performance while "rsa-sha256" is more secure. "rsa-sha1" is recommended.

Certificate File Name/Password/Type:
If you don't have a certificate (private/public key pair) for your domain, DKIM manager will create a certificate for your domain automatically; if you have an existed certificate, please import it from your local disk and input your certificate protection password.

If you choose "you don't have a certificate...", DKIM manager will try to create a certificate from your local machine automatically. If the operation fails, DKIM manager will download a certificate from our server remotely.
If you have another server using our DKIM software to sign the same domain and it uses the same selector, you need to copy the certificate from that server and use the same certificate. Please refer to: Deploy DomainKeys/DKIM on multiple servers with same domain.

If you have another server not using our DKIM software to sign the same domain, please select "I don't have a certificate ...", and use a different selector. To learn more detail, please refer to Selector section.

Signed Headers:
Specify what message headers should be signed. "sender" header and "from" header are a MUST. Using default setting is recommended.

Edited by user Thursday, January 12, 2017 8:51:10 PM(UTC)  | Reason: Not specified

As I introduced "how DKIM works", the recipient mail system need to query public key to verify DKIM signature. So we need to deploy DKIM public key to domain DNS server, then recipient system can query it by DNS server. Now we get back to DKIM manager and select your domain and click "Export Public Key":

Deploy Public Key by DKIM Manager

If your domain is hosted by Windows DNS Server in local LAN. After you added a domain in DKIM Plugin Manager, you can select the domain and click "Deploy Key", input your DNS server address and choose the DNS zone, the public key will be deployed to DNS server automatically.



Deploy DKIM Public Key Manually

If your domain is not hosted by Windows DNS server in local LAN, or it is failed by "Deploy Key" in DKIM manager, you can select the domain and click "Export Public Key". A dialog box will pop up and display a Public Key and a TXT record for deployment in your DNS server.




Here is record detailed information:

TXT Record:
The full name of your public key record.

Public Key:
The value in the record.
Test Mode
"t=y;" in public key record means Test mode, you can remove "t=y;" from your public key record after your DKIM/DomainKeys test is finished.

Domain Policy Record (Optional):
Domain Policy Record is always deployed to _domainkey.yourdomain. In policy record value, o = Outbound Signing policy ("-" means that this domain signs all email; "~" is the default value and means that this domain may sign some email with DomainKeys). If you do not set policy record, the o=~; is used by default.

Edited by user Monday, July 6, 2015 6:33:53 PM(UTC)  | Reason: Not specified

Deploy DKIM Public Key TXT in Network Solutions DNS server or Bind DNS server

If your domain is hosted by NetworkSolutions, you can deploy your public key like this:

Step 1: Select your domain

Step 2: Select the "Edit TXT Record.

Step 3: Copy the value (t=y; k=rsa; p=...) from Public Key field and paste it to the "Text" text box and input "s1024._domainkey" (depends on the information in the dialog box, the syntax is [selector]._domainkey) in Host. Click the "Continue" button.

Step 4 (optional*): Copy the value (t=y; o=~;) from Policy field and paste it to the "Text" text box and input "_domainkey" in Host. Click the OK button.



Deploy DKIM Public Key TXT in other DNS server

If your domain is hosted by other ISP, as most ISP provide DNS Web administration like "network solutions" do, you can refer to "Deploy Public Key TXT in Network Solutions DNS server" section and deploy your public key in your ISP DNS Web administrative tool.

If you are not DNS server administrator, or your domain is hosted by other DNS server, please send the information in dialog box->DNS Public Deployment to your domain DNS server administrator for assistant.

Edited by user Monday, July 6, 2015 6:35:49 PM(UTC)  | Reason: Not specified

DKIM Troubleshooting

If your email doesn't have DKIM-Signature header after you set the DKIM, you should check the followings:

Check your email sender, please make sure your from address is *@yourdomain, and you have set the domain in DKIM. As DKIM signature is based on the email sender, if the sender domain is not set in DKIM Manager, the email won't be signed.

Check your log file for any error message.

If there is error logged, please contact support@emailarchitect.net for assistance.

If there is no error in the log file, you need to verify the DKIM installation.

Installation Permission

When you install DKIM on Exchange Server 2003, please make sure you are using "Domain Administrator" user to run the installer.

Verify IIS SMTP/Exchange 2000/2003 Installation

If you installed EA DomainKeys on Exchange 2003, please open DOS prompt, and change directory to EA DomainKeys installation path\installer.


Please check if there is "EA DomainKeys Sink" installed in the output.




If there is no EA DomainKeys Agent, you can re-run the installer directly (do not uninstall) to fix this problem. You can also contact support@emailarchitect.net for assistance.

Wrong Body Hash

It is likely that the MTA changed email content (disclaimer software or anti-virus software). Please go to DKIM setting, check "Sign a part of message" and set "Maximum length of message body to sign" to zero, then try it again.

Failed to Verify DKIM Signature (wrong body hash, bad signature)

If your email has DKIM-Signature header, but it couldn't be verified by this online tool, you should go to DKIM setting and test your public key again to make sure your public key is ok. If your public key is ok, please contact support@emailarchitect.net for assistance.

Now Exchange Server 2003/2000 can add DKIM signature to outgoing emails from your domain. If you want to send email from other domain, you can simply add the domain from DKIM manager.

Edited by user Monday, July 6, 2015 6:37:58 PM(UTC)  | Reason: Not specified

Using a single DKIM selector with the same domain on multiple Exchange Servers

If all of your servers are running with EA DKIM, you should deploy the certificate as follows: First of all, install EA DKIM on the first server, and create the certificate for the domain. Then install EA DKIM on other servers, and copy the *.pfx certificate you created on the first server to other servers under EA DKIM installation path\certs. Finally, when you create the DomainKeys/DKIM on other server, please have "I have a key pair certificate ..." selected, and import the *.pfx file from your local disk and input the "TMP001" (default password) as the password. All of your servers will have the same certificate (private/public key pair) for your domain. Please also make sure you use the same selector "s1024" (default name).



Since the private/public key pair is stored in the certificate, if you use the same selector/certificate for the same domain on multiple servers, all servers will use the same key pair for this domain. You just need to deploy the public key to "selector._domainkey.emailarchitect.net", every email from multiple servers can be verified by this public key.

Edited by user Monday, July 6, 2015 6:38:27 PM(UTC)  | Reason: Not specified

Using DKIM Sender Rule

Sometimes you need to send an email with sender address not hosted by your server. In this case, you cannot set DKIM signature for such email, as you don't have permission to deploy the DKIM public key to the domain not hosted by your DNS server.

The typical usage is email forwarding. For example, one remote email is delivered to your local user mailbox, but your local user set email forwarding to another remote address. With sender rule, you can re-sign DKIM by your domain and also change MAIL FROM to comply with SPF record.

If you don't send email from outside email address, or you don't need to sign the DKIM for those emails, you can simply ignore this topic.

How to use Sender Rule

Here is the scenario. You own a domain "emailarchitect.net" and you have DKIM/DomainKeys for "emailarchitect.net" set on your server. There is no problem when you send emails with sender "*@emailarchitect.net", the email will be signed correctly. At the same time, your customer requested you to send emails with sender "*@adminsystem.com" and sign the DKIM/DomainKeys signature for outgoing emails. As "adminsystem.com" is your customer domain and you don't have permission to deploy the public key to "adminsystem.com" DNS server, you have to use sender rule.



To solve the problem, you can add a sender rule like the above screenshot. This rule means "If from addess is *@adminsystem.com, then add a sender header (Sender: testuser@emailarchitect.net) to the message". And the email will be signed by "emailarchitect.net" based on the sender header.

With the above sender rule, the email will be signed by DomainKeys/DKIM signature with domain "emailarchitect.net". And the recipient email client will display "From: testuser@emailarchitect.net on behalf of *@adminsystem.com".

Use Reply-To header instead of Sender header

If you also check "Use Reply-To header instead of Sender header", And the recipient email client will display:

From: testuser@emailarchitect.net, Reply-To: *@adminsystem.com (original sender address)
We strongly suggest that you use this option for anti-spam policy.

DKIM Priority

DKIM setting has higher priority than sender rule, that means if DKIM setting is found for the email, this email will not be changed by sender rule.

For example, if you set "emailarchitect.net" in DKIM setting, and add a rule like this: "if From contains *@emailarchitect.net", then ...". Sender rule won't change the email sender from *@emailarchitect.net, the email will be simply signed by DKIM with "emailarchitect.net".

Edited by user Monday, July 6, 2015 6:39:47 PM(UTC)  | Reason: Not specified

Thank you for the exhaustive post. But I'm a newby on DKIM, my situation is this: exchange server 2003 on static ip xxx.xxx.xxx.xxx; DNS manage on provider Aruba where mx dns mysite.com head to xxx.xxx.xxx.xxx. I had a lot of problem with emails deliverability so I started using TurboSMTP, turboSMTP offer DKIM key so I would like to set up DKIM on my email process, but I don't know where I have to operate, on my DNS provider or on my exchange server? If the answer is on DNS provider I can do nothing because Aruba only offer SPF record manage.

Thank you for the answer.

Edited by user Tuesday, November 19, 2013 2:48:31 AM(UTC)  | Reason: Not specified

See Also:

Set DKIM record in Bind DNS server

Aug 16, 2015
DomainKeys/DKIM for IIS SMTP Service and Exchange Server 3.3

Supports certificates in machine store and email address wrap;

Bug fix for Sender Rule in IIS SMTP Service.