For increasing size of attachments to 50 MB in Zimbra, a few settings need to be altered as follows:
Postfix configuration (zimbraMtaMaxMessageSize and message_size_limit)
You can examine the current value of this parameter like this:
# su - zimbra
$ postconf message_size_limit
message_size_limit = 10240000
This configuration parameter is stored in the zimbra ldap directory, and propagated to postconf’s message_size_limit by zmmtaconfig, which is invoked by the zimbra postfix command. The following commands will set the message_size_limit to 2MB (adjust this value to suit your needs):
# su - zimbra
$ zmprov modifyConfig zimbraMtaMaxMessageSize 52428800
$ postfix reload
You can then confirm the changes with this command:
$ postconf | grep message_size_limit
Change the limits in Zimbra configuration for all types of files uploads.
$ zmprov modifyConfig zimbraFileUploadMaxSize 52428800
$ zmprov ms `zmhostname` zimbraMailContentMaxSize 52428800
$ zmcontrol restart