Axigen might be a bit more popular than SOGo. We know about 1 link to it since March 2021 and only 1 link to SOGo. We are tracking product recommendations and mentions on various public social media platforms and blogs. They can help you identify which product is more popular and what people think of it.
Episode 3, which I will bookmark as it lists the solutions that they have selected. I read e.g. About SOGo and Zorin OS that I didn't know of. Source: about 1 year ago
I am the CEO of Axigen (axigen.com) and we have finally finished the complete process to have our trademarked logo published with a valid corresponding VMC certificate as a BIMI DNS record. Source: over 2 years ago
Roundcube - Web-based IMAP email client
mailcow - An open source mailserver suite.
Zimbra - Zimbra is trusted by over 500 million users to increase productivity with a complete set of collaboration tools while maintaining total control over security and privacy.
Rainloop - RainLoop is a web based email client.
hMail Server - hMailServer is a free e-mail server for Microsoft Windows.
iRedMail - A fully fledged, free email server solution, an open source project (GPL v2).