Dear all,
SOGo team removed nightly builds for SOGo v4 + v3 permanently:
https://sogo.nu/bugs/view.php?id=5157
You should update yum/apt repository files and switch to SOGo v5:
Upgrading is simple, no SQL structure changes from v4 to v5.
On CentOS, please update file /etc/yum.repos.d/sogo.repo, replace version number "4" by "5", then run "yum clean metadata && yum update".
On Debian/Ubuntu, please update file /etc/apt/sources.list.d/sogo.list (or sogo-nightly.list), replace version number "4" by "5", then run "apt-get update && apt-get upgrade".
If your server was deployed with iRedMail Easy[1] platform, re-deploying SOGo will switch to v5 automatically.
[1] iRedMail Easy platform: https://www.iredmail.org/easy.html