While working with Zimbra collaboration suite, I figured out today that I needed to increase the attachment size limit of the message to send larger messages. The default attachment size limit is 10MB. Even if the attachment is a little less than 10MB, it won’t send the same error that the maximum message size is crossing the limits. This is because Zimbra MTA will encode the message into base-64 encoding. With base64-encoding, the message size becomes larger than 10MB. So here is the command I used to increase the limit from 10MB to 20MB.
If you want to change the default Zimbra message size limit, it is important to understand that there are two parameters: email content maximum size and file upload size. The total message size limit is determined by the zimbramailcontentmaxsize parameter, while the file upload size is determined by the upload size parameter.
Increase Message Size Limit and Attachment File Upload Size in Zimbra MTA
To modify both parameters, we have to use the zmprov command with the modifyconfig option. With this command, we can set different values for each parameter depending on our needs and preferences.
Here is the command to increase the limit from 10MB to 20MB.
[root@mail ~]# su zimbra
[zimbra@mail root]$ zmprov mcf zimbraMtaMaxMessageSize 20480000
[zimbra@mail root]$ zmprov mcf zimbraFileUploadMaxSize 20480000
If you’re using Zimbra with Postfix, you should use the following command:
# su – zimbra $ postconf message_size_limit message_size_limit = 20480000
# su – zimbra $ zmprov modifyConfig zimbraFileUploadMaxSize 20480000
$ postfix reload $ zmcontrol restart
20480000 is the message size in bytes. To revert back to the 10MB upload size limit, set the size to 10240000. No need to restart Zimbra Server… Now you can send messages up to 20MB.
Note: Usually it is not recommended to increase the size of the message to a large message size limit, as it will slow down the server performance.
This fully explains how to adjust the Maximum Message Size and Maximum File Upload Size for messages passing through Zimbra mail.