The issue is on Viux: they need to update AT LEAST to the latest stable version v.8664 (16.3.6989 is an OLD version, and many new features and bug fixes are waiting on the newest... Not mentioning the new BETA...)
Gabriele Maoret - Head of SysAdmins at SERSIS
Currently manages 6 SmarterMail installations (1 in the cloud for SERSIS which provides services to a few hundred third-party email domains + 5 on-premise for customers who prefer to have their mail server in-house)