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Encryption for data-in-transit

In addition to protecting customer data at rest, Microsoft uses encryption technologies to protect customer data in transit. Data is in transit:

  • When a client machine communicates with a Microsoft server;
  • When a Microsoft server communicates with another Microsoft server; and
  • When a Microsoft server communicates with a non-Microsoft server (for example, Exchange Online delivering email to a third-party email server).

Inter-data center communications between Microsoft servers take place over TLS or IPsec, and all customer-facing servers negotiate a secure session using TLS with client machines (for example, Exchange Online uses TLS 1.2 with 256-bit cipher strength is used (FIPS 140-2 Level 2-validated). (See Technical reference details about encryption for a list of TLS cipher suites supported by Microsoft 365.) This applies to the protocols that are used by clients such as Outlook, Skype for Business, Microsoft Teams, and Outlook on the web (for example, HTTP, POP3, etc.).

The public certificates are issued by Microsoft IT SSL using SSLAdmin, an internal Microsoft tool to protect confidentiality of transmitted information. All certificates issued by Microsoft IT have a minimum of 2048 bits in length, and Webtrust compliance requires SSLAdmin to make sure that certificates are issued only to public IP addresses owned by Microsoft. Any IP addresses that fail to meet this criterion are routed through an exception process.

All implementation details such as the version of TLS being used, whether Forward Secrecy (FS) is enabled, the order of cipher suites, etc., are available publicly. One way to see these details is to use a third-party website, such as Qualys SSL Labs. Below are the links to automated test pages from Qualys that display information for the following services:

For Exchange Online Protection, URLs vary by tenant names; however, all customers can test Microsoft 365 using microsoft-com.mail.protection.outlook.com.