If you ever need to downgrade IceWarp EPOS to the previous version, please consult your decision with our technical support team first. We will do our best to resolve any issues you might face on IceWarp EPOS.
In general, though, please note that downgrading to an older version is possible only if you have a backup of the previous version (must be the last backup of Deep Castle 2 before the upgrade) due to significant changes in the configuration where some elements used to be stored on a filesystem and now they are stored in the database. That causes the database to be not backwards compatible.
The only possible way to get back to the previous version is to install IceWarp from scratch again and restore data from a backup consisting of a complete backup of the IceWarp directory and a dump of all the databases used in IceWarp.
If you run the installer of any older version over the existing IceWarp EPOS installation, you will lose data, and IceWarp will become unusable. Changes made in the databases are irreversible after the upgrade to IceWarp EPOS.
In any case, please don't hesitate to contact our support to find out more.