Mailspring vs GyazMail

Mailspring has great integration with gmail features and tags.

The UI is very well designed and neat.

Activity tracking is built into Mailspring so you get notified as soon as contacts read your messages and can follow up appropriately.

Mailspring uses a C++ sync engine designed to be as efficient as possible, so you can leave the app running and not see your laptop battery life drain away.

Using a single inbox for all of your email accounts helps you get more done in less time. Mailspring supports every major mail provider—Gmail, iCloud, Office 365, Outlook.com, Yahoo!, and IMAP/SMTP—so you have a single, streamlined command center for all your messages.

You can swipe to archive / snooze messages and specify when you'd like them to resurface in your inbox.

Only in the paid version though.

Goichi Hirakawa, the main developer of GyazMail, has been committed to his project since 2003 and delivers updates regularly.

The user can define complex mail sorting rules for incoming and outgoing mail.

As of v1.6

GyazMail is a native macOS application, based on the Cocoa API.

the mailbox view is very comfortable

GyazMail is a Japanese product, so it has very good support for Asian languages.

GyazMail is available for all versions of Mac OS X / macOS starting with version 10.1

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.

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.