Use Mail extensions in Mail on Mac

Compose extensions can help you write messages. For example, validate recipients’ email addresses as you enter them, or add headers to certain messages. If an extension’s icon isn’t available in the Compose window toolbar, you can customize the toolbar to add it.

Action extensions can help you manage your inbox. For example, flag certain messages or move them to another mailbox, such as the Junk or Archive mailbox. If an extension performed an action on a message, the Extension icon is shown in the message header.

Content blocker extensions can help protect your privacy. For example, prevent remote content (such as images) from being loaded when you read messages and used to let senders learn your Mail activity.

Security extensions can help you encrypt, decrypt, and sign messages. If an extension has the information it needs to encrypt or sign a message you’re writing, an encrypted icon (a closed lock) or a signed icon (a checkmark) appears in the message header.