# decodedMessage(forMessageData:) Decrypts message content and details about digital signatures. ``` func decodedMessage(forMessageData data: Data) -> MEDecodedMessage? ``` ## Parameters `data` The raw MIME message data, which may be encrypted or signed. ## Return Value An object that represents the decoded message, or `nil` if the message isn’t encrypted or signed. ## Discussion When MailKit needs the original unencoded data for a message, it invokes this method and passes the raw MIME data for the message. If you determine that the message isn’t encoded and your extension doesn’t need to do anything, return `nil,` and MailKit decodes the message data normally. If you inspect the message data and determine that you need to decode it, create an instance of [`MEMessageSecurityInformation`](/documentation/MailKit/MEMessageSecurityInformation) that describes the message’s signed and encrypted status. If the message is signed, specify an array of [`MEMessageSigner`](/documentation/MailKit/MEMessageSigner) objects to indicate who signed the message. [`MEMessageSigner`](/documentation/MailKit/MEMessageSigner) includes additional context that the security handler’s view controller uses to display details to the user, such as the certificate a signer used. To provide the decoded message content to MailKit, create an instance of [`MEDecodedMessage`](/documentation/MailKit/MEDecodedMessage). The decoded message contains the raw MIME content for the message, and the message security information. > Important: > If decrypting the message fails, or the digital signature isn’t valid, include an error object with a localized description of the failure in the ``doc://com.apple.mailkit/documentation/MailKit/MEMessageSecurityInformation``. Mail uses this description to inform the user of the issue. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)