When comparing Mail.app vs Airmail, the Slant community recommends Airmail for most people. In the question“What are the best e-mail clients for macOS?” Airmail is ranked 2nd while Mail.app is ranked 3rd. The most important reason people chose Airmail is:
Airmail has a very clean and modern interface. On the left side of the screen are the folders (inbox, starred, draft, sent, snooze, trash) and on the right side the email threads for the folder currently being viewed.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Integration (with other Apps/Hardware)
One thing Apple does well is to integrate its apps and hardware. The mail app is no exception. If you must be in the hermit kingdom, at least take advantage of the (often excellent) features provided.
Pro Will probably be enough for a sizable chunk of users
Since it's the built-in Mac email client and is quite complete feature-wise, most users will not really need any other third-party applications out there. Mail.app should be enough for their needs.
Pro Easily annotate pictures or sign documents inside the client itself
Mail.app has powerful markup tools which let users add annotations to images or even sign documents they got through email without ever leaving the client.
Pro Smart folders on steroids
- You can choose out of tenths of mailheaders (several hundreds including virtual headers)
- "<header> is (not) in <folder> <header>" operator which enables you to do cool filters
- Each smart folder can have smart subfolders by an user definable key
Pro Shows threaded view with snippets in middle panel
Pro Can be easily extended
If the basic features inside Mail.app are not enough, it can easily be extended through plugins to add new features.
Pro Clean interface
Airmail has a very clean and modern interface. On the left side of the screen are the folders (inbox, starred, draft, sent, snooze, trash) and on the right side the email threads for the folder currently being viewed.
Pro Integrates with multiple third-party services
Airmail can integrate with multiple Cloud services for syncing, creating backups, adding tasks and more. Some of these services include Dropbox, Box, Fantastical, 2DO, Todoist, Wunderlist etc.
Pro Automatically syncs settings between devices
If you are using Airmail in different devices (either MacOS or iOS), you can automatically sync settings through iCloud.
Pro Consistent interface between devices
Airmail is available for both iOS and Mac, for people who use Apple's mobile devices. And the interface between both platforms is quite consistent, making it easy to seamlessly jump between one and another.
Pro Fast and easy setup process
Even though there's a huge amount of settings available, it's quite easy to get used to each of them and the setup process is very fast and easy.
Pro Support for VIP folders
VIP folders are for particular senders which you always want to read even when you are ignoring email. The way it works is that you add different senders as VIPs and emails from those senders will always be surfaced on top of everything else.
Pro Extremely customizable
Instead of forcing the user to work with their email the way Airmail developers would want, it allows the user to customize and make the email client work the way they want because of the sheer flexibility of the application.
There's a lot of settings available in Airmail with which you can customize almost every aspect and functionality of the app. In fact, it's very easy to get lost in them and spend a lot of time tweaking and customizing everything to your liking.
Pro Supports Gmail shortcuts
Pro Multiple ways of sorting emails
There are multiple ways to sort emails with Airmail. You can sort by unread, starred, attachments, conversations, dates, and many more criteria. You can even combine different criteria together.
Using these filters makes it extremely easy to quickly find any email you are looking for.
Pro Always keep the inbox clean
Airmail allows users to snooze an email until a defined moment (a few hours later, tomorrow, next weekend, next week, etc.), allowing you to process every email immediately and to always keep the inbox clean.

Pro Supports trackpad gestures
Airmail is able to use trackpad gestures for achieving and deleting mail items.
Cons
Con No option to snooze emails
You can not snooze emails to view later. This makes it hard to keep the inbox clean at all times since you have to read every email and choose to delete or keep them the moment they arrive to do so.
Con Missing lots of advanced features
Out of the box, Mail.app may not have as many features as some other options. This can be mitigated with plugins though. But that is not a perfect solution since third-party plugins may not be very reliable in the long run.
Con Really bad reliability
Database engine gets stuck consuming 100% of one core; crashes; a 40GB log file has been spotted.
Con Updates may break plugins
Apple is known to make API changes to Mail.app when updating which break a lot of plugins.
This can be very annoying for users whose workflow heavily relies on plugins, since they have to wait for plugin developers to make the changes needed to fix any issues brought by the update.
Con Poor performance for some users on El Capitan
Con Ugly
Con Poor calendar integration in exchange mode
Con Unreliable
There are many issues/bugs with different accounts, including Gmail and iCloud.
Con Serious sync problems
On some IMAP accounts, there are a number of serious sync problems, which otherwise work fine with Apple Mail.
Con Search is buggy and not very powerful
Con Not free
Paid version only.
Con iOS app requires a subscription to enable incoming mail notifications
The iOS app now requires a subscription to enable incoming mail notifications. This makes the iOS app very unattractive and there's little point installing the Mac desktop client for users who want to sync accounts between devices.

Con Copying/moving mails unreliable
Doesn't work most of the time even though the operation is reported as successful. Even has lost emails when moving. Support was not too much use either.
Con Rather expensive
Con Inability to turn off auto-creation of labels
Version 3 does not allow it while version 2 did.
Con UI is a little busy
Con Has the "slow typing" bug
When composing an email, Airmail can respond very slowly to keystrokes. Customer service refuses to acknowledge this problem, responding that it's "not real" - which is a very odd response, to simply refuse to acknowledge the customer's experience.
