Through zimbraGUI didn’t find it how to do it, but through console it appeared to be working with the following set of commands to modify postfix actually-
su zimbra zmprov mcf zimbraMtaMaxMessageSize 20971520 zmprov mcf zimbraFileUploadMaxSize 20971520 zmprov mcf zimbraMailContentMaxSize 52428800 zmprov modifyConfig zimbraMtaMaxMessageSize 52428800 postfix reload
Once theyre executed, restart the server (restarting zimbra won’t reflect the changes made, so need a fresh reboot of OS)
