When comparing Airmail vs GyazMail, 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 GyazMail is ranked 6th. 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 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 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 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 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 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 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.
Pro Long term support and development
Goichi Hirakawa, the main developer of GyazMail, has been committed to his project since 2003 and delivers updates regularly.
Pro Mail sorting rules
The user can define complex mail sorting rules for incoming and outgoing mail.
Pro 64-bit support
As of v1.6
Pro Native Cocoa API based
GyazMail is a native macOS application, based on the Cocoa API.
Pro customizable fonts & colors
the mailbox view is very comfortable
Pro Very good support for Asian languages
GyazMail is a Japanese product, so it has very good support for Asian languages.
Pro Supports older versions of macOS
GyazMail is available for all versions of Mac OS X / macOS starting with version 10.1
Pro Freely selectable hard line wrap
In GyazMail you can set a maximum number of characters per line. The program will wrap the lines using hard wrapping on sending. This feature is very useful for newsgroups that require a hard break after 72 characters.
Pro Supports a big variety of character encodings
Uses Oniguruma regular expression library, which is a very elaborate regular expression engine that supports a big variety of character encodings. This makes very much sense with e-mail, as in an e-mail theoretically any character encoding could be used. Because it is free software (BSD), written in C, very elaborate, stable and still actively maintained it is also used in Atom, Take Command Console, Tera Term, TextMate, Sublime Text, SubEthaEdit, and jq.
Cons
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.
Con Looks old and outdated
Con If connection drops or times out, Gyazmail just sits there until you click OK button
Con Cannot remove attachments to save space
Con Still a 32-Bit app
