Microsoft Exchange®: Email authentication with DKIM

This article explains what DKIM is, and when it is utilised for sending emails through Microsoft Exchange with IONOS.

Microsoft Exchange will use DomainKeys Identified Mail (DKIM) when sending emails, starting on November 12, 2025. With this innovation, we are increasing the security of your mailboxes, and ensuring that your emails continue to arrive reliably.

DKIM (DomainKeys Identified Mail) is a technical authorisation method that adds an invisible digital signature to your emails. This confirms to the recipient that an email really comes from you, and prevents fraudsters from sending spam or phishing emails in your name.

Together with SPF and DMARC, DKIM reduces the likelihood of your emails being marked as spam and makes an important contribution to curbing mail spoofing and spam.

You do not need to do anything to benefit from these changes. Authorisation via DKIM takes place automatically in your Microsoft Exchange. In some cases, this function remains inactive as emails cannot be signed with DKIM via the following delivery channels:

• Exchange accounts configured via IMAP/POP: We recommend that you use your account directly with Exchange to benefit from maximum security. Step-by-step instructions can be found in the following category in the Help Centre article Microsoft Exchange.
  
  If you have configured your Exchange account via IMAP/POP and now want to use it as a Microsoft Exchange account, you should back up your data before switching over. You can find step-by-step instructions for Outlook 2016, 2019 and 2024 in the article Backing up and restoring an email account with Microsoft Outlook.
• Accounts that use an external email address (e.g. gmail.com): We recommend that you move these accounts to an email address with its own domain in order to activate DKIM. You can also find step-by-step instructions for this in our Help Centre article Microsoft Exchange: Change email address.
• System-generated emails, such as out-of-office notifications.