IceWarp using seven separate databases. By default, all databases are saved in SQLite except accounts saved on the file system in .cfg files. That's why the migration steps are different.
1. Navigate to administration console - System - Storage - Accounts.
2. If you can see that accounts are saved on "File System", select "DB Settings..." otherwise your accounts are saved in some DB and you can use the Database migration tool.
3. Setup connection to DB. In the example below IceWarp connecting to MySQL DB located on IP 127.0.0.1 using port 3306 with user Icewarp and password. Use the "Test Connection" button to check if credentials are correct.
4. Click on "Create Tables" which will create all required tables on the database.
5. After creation you will receive a prompt to migrate accounts/domains to a newly created database. Select Yes.
6. After converting, switch the option from "File System" to "Database". After applying the change the restart of all modules is necessary.
7. In case you are registering issues (you cannot log in) after the migration you can always switch back from "Database" to "File System". For switch you can use IceWarp tool.sh/tool.exe. API variable for accounts is "C_System_Storage_Accounts_StorageMode" (0 - Professional file system, 1 - Standard file system, 2 - ODBC).
/opt/icewarp/tool.sh set system C_System_Storage_Accounts_StorageMode 1
C:\Program Files\IceWarp\tool.exe set system C_System_Storage_Accounts_StorageMode 1