That being said, all webmail clients are terrible IMHO as they usually neglect their search features (e.g. fulltext search is slow, you can’t search across folders; Cloudron‘s „virtuall all mail folder“ could help but throws off iOS mail) or have the plugin disease (essential features like MFA are outsourced to a plugin, see Roundcube).

It‘s a sad state of affairs. For my personal mail, I either rely on desktop software / a mobile device or - if I need to have access to my mail the web when I’m not at home, I use Vivaldi Mail in a local Ubuntu Container to which I connect via Apache Guacamole.

That being said, since mailboxes are really hosted by Cloudron under the hood, I think RC and Sogo can be hosted as mail client apps at the same time. Offering RC to "simple" users and Sogo (with ActiveSync) to "power" users, while hosting both on the same Cloudron.

As mentioned earlier by @andreasdueren, the ActiveSync support is a strong point for SOGo.

I also took note of @fbartels’s comment that Roundcube generally feels faster and lighter compared to the Mail app in Nextcloud.

To better understand the security aspect, I asked ChatGPT and Gemini about Roundcube vs SOGo.

Based on their answers and some public vulnerability data, the rough conclusion I got is:

• SOGo appears to be “more secure” than Roundcube if we look purely at the frequency and severity of reported vulnerabilities,
• For example, there have been fewer recent high‑impact issues (such as major RCE vulnerabilities) publicly associated with SOGo than with Roundcube.

Do you agree with this assessment, or is there important context I might be missing?

Thank you again for all the insights shared so far. They’ve been very helpful.