To enable the Out of Office (Vacation) tab in SOGo perform the following actions:
NOTE: I am told this will overwrite any sieve mail filter already set (unverified)
sudo mkdir /etc/zentyal/stubs/sogo
sudo cp /usr/share/zentyal/stubs/sogo/sogo.conf.mas /etc/zentyal/stubs/sogo/sogo.conf.mas
sudo nano /etc/zentyal/stubs/sogo/sogo.conf.mas
CTRL w to open "find" and search for:
Vacation (Line should read, "SOGoVacationEnabled = No;"
Change No; to Yes;
CTRL o to save
CTRL x to exit
Restart SOGo from the web interface