Apple Mail Quick Start
You can jump directly to any topic of interest, but I suggest starting with the first few chapters to get a solid foundation. Chapters are marked with [macOS] and/or [iOS] to show the platforms they cover.
Understand what you’re dealing with:
Discover Mail’s new features and design changes. Read Learn What’s New in Mail. [macOS/iOS]
Get a grip on POP, IMAP, SMTP, Exchange, and more as you Learn About Email Protocols. [macOS/iOS]
Make sure you understand account-setup details and how Mail deals with common tasks. See Master Mail Concepts. [macOS]
Find the ideal Mail setup for your needs:
Tailor Mail to your needs and tastes with settings, shortcuts, plugins, and more as you Customize Mail. [macOS]
Take Mail even further. See Extend and Automate Mail. [macOS]
Gmail user? You’re in for some weirdness, so there’s a whole chapter just for you: Use Gmail with Mail. [macOS]
Become a better Mail user:
Search like a pro. Read Find Your Messages. [macOS]
Manage incoming and saved messages as you Take Control of Your Inbox, and then learn the best ways of sending and replying to email in Become a Better Correspondent. [macOS/iOS]
Handle exceptional tasks:
For enhanced privacy, Sign and Encrypt Messages. [macOS/iOS]
Perplexed by an error message or other misbehavior in the Mac version of Mail? Read Fix Mail Problems. [macOS]
Make the most of Mail on your iPhone, iPad, or iPod touch. See Use Mail in iOS. [iOS]