GyazMail

GyazMail is an email client for macOS, developed and being maintained by Japanese programmer Goichi Hirakawa. It supports the POP3, IMAP and SMTP protocols. Its handling of multiple email accounts includes local mailboxes.
Gyazmail is based on the native macOS Cocoa and written in Objective-C. For its search function, GyazMail uses the Oniguruma regular expression library, which supports a variety of character encodings, which is especially relevant for Asian languages.
Version 1.0.1 was released in 2003. 