# MEComposeSessionHandler An object that participates in the composition of mail messages, and annotates recipient tokens. ``` @MainActor protocol MEComposeSessionHandler : NSObjectProtocol ``` ## Overview When the user composes a message, MailKit requests a compose session handler object from your extension. MailKit uses this handler in the following ways: - To inform it when the compose session begins and ends - To add status annotations for email addresses that the user enters into the To, Cc, and Bcc fields - To display a custom popover in the compose window - To include custom headers in an outgoing message - To confirm that an outgoing message is ready for delivery Each of the items in the list above corresponds to methods that the handler implements. To indicate that your extension contains a compose session handler, add `MEComposeSessionHandler` to the array in the extension’s `Info.plist` file: ```swift NSExtensionAttributes MEExtensionCapabilities MEComposeSessionHandler ``` ## Topics ### Handling Compose Sessions [`MEComposeSession`](/documentation/MailKit/MEComposeSession) An object that represents a single mail compose window. [`- mailComposeSessionDidBegin:`](/documentation/MailKit/MEComposeSessionHandler/mailComposeSessionDidBegin(_:)) Informs the handler when the user opens a compose window. [`- mailComposeSessionDidEnd:`](/documentation/MailKit/MEComposeSessionHandler/mailComposeSessionDidEnd(_:)) Informs the handler when the user closes a compose window. [`MEComposeSessionError`](/documentation/MailKit/MEComposeSessionError) An error that indicates the compose session is in an erroneous state. ### Annotating Email Address Tokens [`- session:annotateAddressesWithCompletionHandler:`](/documentation/MailKit/MEComposeSessionHandler/annotateAddressesForSession(_:completion:)) Indicates whether recipients in the compose window are valid or not. [`MEAddressAnnotation`](/documentation/MailKit/MEAddressAnnotation) An object that indicates the validity of an email address. ### Extending the Compose Window Interface [`- viewControllerForSession:`](/documentation/MailKit/MEComposeSessionHandler/viewController(for:)) Provides a custom view controller to display as part of the compose window. ### Adding Custom Headers [`- additionalHeadersForSession:`](/documentation/MailKit/MEComposeSessionHandler/additionalHeaders(for:)) Provides custom headers to include in the outgoing message. ### Approving Message Delivery [`- session:canSendMessageWithCompletionHandler:`](/documentation/MailKit/MEComposeSessionHandler/allowMessageSendForSession(_:completion:)) Confirms that the message is ready for delivery. ## Relationships ### Inherits From [`NSObjectProtocol`](/documentation/ObjectiveC/NSObjectProtocol) --- 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)