How to discover Email forwading

[bellzerr]

Old boss used to have various email accounts forwarded to him for various reasons. New boss wants to know whose mail is being monitored. Without check EVERY account, how can I query to discover ALL the accounts which are being forwarded to a given email account?
Or... how can I query to discover ALL account that are being forwarded to ANY other account?

[vaidotas]

Find "Forwarding addresses hidden from the user"
zmprov -l gaa -v | egrep '# name|zimbraMailForwardingAddress' | grep -v Max | grep -B 1 "zimbraMailForwardingAddress"