Apps Related to Message Filtering

Icedove is a robust and adaptable open-source email client forked from Mozilla Thunderbird, offering comprehensive email management, RSS feed aggregation, integrated chat, and extensive customization options through extensions.

Opera Mail, formerly known as M2, is a versatile and lightweight email and news client developed by Opera Software. It offers a unified approach to managing email, news feeds, and contacts with a strong emphasis on organization and speed.