Content Encoding Error in plesk webmail for customers in Middle East
“Content Encoding Error (content_encoding_error)”
Really astonished in hearing such a issue with plesk horde that only a regional customers are affected with this error. This eventually found to be a bug in Horde content copmression code and have resolved by disabling this feature.
$conf['compress_pages'] = false;
in webmail/horde/config/conf.php.