NethServer 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
Check out Nethserver - https://nethserver.org/. Source: over 2 years ago
Roundcube - Web-based IMAP email client
Zentyal - Linux directory, domain, mail, gateway and infrastructure server for SMBs.
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.
ClearOS - A very good alternative for Windows Server, for free
Rainloop - RainLoop is a web based email client.
pfSense - pfSense is a free and open source firewall and router that also features unified threat management, load balancing, multi WAN, and more