Error «Wrong ‘mbstring.func_overload’ option value» when opening Roundcube

Symptoms

When opening the Roundcube mail client, the following error is displayed in the browser:

«ERROR: Wrong ‘mbstring.func_overload’ option value and it wasn’t possible to set it to required value (0). Check your PHP configuration (including php_admin_flag).»

Causes

In PHP 7.4.33 settings, the value of the mbstring.func_overload parameter does not equal 0.

Solution

Starting with ispmanager version 6.107.0, Roundcube operates using an alternative version of PHP 7.4.33

Go to the PHP section, select the version «7.4.33 (alt)» and click Extended settings, then change the value of the mbstring.func_overload parameter to 0.

If a different value for this parameter is required for a specific site, set it in the individual PHP settings in the Sites section by selecting the site and clicking the PHP button.