can u test this rpm
yum install http://mirror.de-labrusse.fr/NethDev/nethserver-sogo/nethserver-sogo-1.6.12-1.ns7.sdl.noarch.rpm
config setprop sogod IMAPLoginFieldName mail
signal-event nethserver-sogo-update
then all values ‘userPrincipalName’ will be changed to ‘mail’
for reversing
config setprop sogod IMAPLoginFieldName ''
signal-event nethserver-sogo-update
or
config delprop sogod IMAPLoginFieldName
signal-event nethserver-sogo-update