You can't directly block contacts within Apple Mail. Apple Mail is an email client, and blocking contacts is typically a feature associated with communication apps like Messages or Phone.
To block a contact, you'll need to use the built-in blocking features within your iPhone or iPad settings:
- Open the Settings app on your iPhone or iPad.
- Tap on "Phone" or "Messages" depending on where you want to block the contact.
- Scroll down and tap on "Blocked Contacts".
- Tap on the "+" icon to add a new blocked contact.
- Select the contact you want to block from your contact list.
Once you've blocked a contact, they will no longer be able to send you messages, calls, or FaceTime calls. You can also unblock contacts by following the same steps and tapping on the "Edit" button at the top right corner of the screen.