Digitally sign your IIS SMTP outgoing emails, making their origin and content trustworthy while improving your reputation and helps to prevent them from being flagged as spam by services such as Hotmail, Yahoo Mail and Gmail. DKIM provides businesses an industry-standard method for mitigating email fraud and protecting an organization's brand and reputation.

ThinkDKIM hooks itself to the SMTP service pipeline, adding a special header field containing a digital signature of the message content using a pre-defined private key. Verifiers like Hotmail, Yahoo Mail and Gmail will later on recover the matching public key from a pre-defined DNS TXT record, and verify the message origin and integrity.

ThinkDKIM for IIS SMTP Manager

Key Features

  • DomainKeys Identified Mail (DKIM) Signatures (RFC 6376), see
  • Unlimited number of DomainKeys
  • Intuitive installation and management interface
  • Optionally exclude certain header fields from signature, enabling Amazon SES support etc.

Supported Platforms

  • Microsoft Windows Server 2008 R2/2012/2012 R2/2016/2019/2022 (x64)
  • IIS with the SMTP Server feature installed




License Price
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Trial License - Try Before You Buy
Allows unlimited domain keys on a single server for 30 days
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Standard License
Allows unlimited domain keys on a single server
199.95 USD PayPal
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Enterprise License
Allows unlimited domain keys on multiple servers
499.95 USD PayPal
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"... this product turns out to be a lifesaver! ... tried another, similar product with mixed results"
Phil Hamsey, REMS Systems Manager

"... easy to setup and use, and support has been fantastic. Thank you for providing this valuable tool."
George Rulon Myers, Director of Engineering, CrystalGraphics, Inc.

"ThinkDKIM for IIS SMTP has lifted our rating and successfully reduced bounces."
David Eedle,

What's DKIM?

DomainKeys Identified Mail (DKIM) is a method for associating a domain name to an email message, thereby allowing a person, role, or organization to claim some responsibility for the message. The association is set up by means of a digital signature which can be validated by recipients. Responsibility is claimed by a signer —independently of the message's actual authors or recipients— by adding a DKIM-Signature: field to the message's header. The verifier recovers the signer's public key using the DNS, and then verifies that the signature matches the actual message's content... Wikipedia