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In Exchange one of the most common changes from the default that is required by business need is to increase the default allowed message size. This seems like a simple task, but in an attempt to make this type of setting as flexible as possible it must be set in at least two locations, with the potential for many more. Below I’ll outline each of the locations to change this setting both in the Exchange Management Console (EMC) and the Shell.
Outbound Send Connector(s) ^
To begin with Exchange 2010 separates the setting for inbound and outbound mail. In Exchange terminology these are referred to as Send and Receive Connectors. For each of these connector types you can have multiple connectors, each having their own message size restriction. In the case of the Send Connector this is done so you specify different settings depending on the external domain. For example you may want to allow 30 MB message to go out by default but if you have a connector to a well connected partner organization allow up to 50 MB.
In EMC you change this setting in Organization Configuration> Hub Transport> Send Connectors section. If you double click on each of your connectors (most of you will probably only have one) you will see a “Maximum Message Size” setting.
Exchange maximum message size - Send-Connector
To perform this same task from the Exchange Shell you only need the following command, changing the connector’s name and the size you want to set.
Set-SendConnector "Outbound" -MaxMessageSize 50MB
If you think about it in a situation where you have many connectors this can be extremely handy because you can cut and paste multiple commands and keep the mouse click count down.
Receive Connector(s) ^
Receive connectors are the same idea as Send connectors, but for the inbound messages. By default you’ll have two of these, “Client MAIL” which handles inbound messages from the individual Outlook or OWA clients, and “Default MAIL” which handles mail from anyone else. In some situations you may want to lock this down tighter. In my corporate environment the Default MAIL connector will only accept mail from the IP of my spam filtering appliance, and then have a separate connector for devices within my organization which I would like to relay.
Again in the configuration of each of these connectors you set a “Maximum Message Size” like seen below. The setting is changed at Server Configuration> Hub Transport> Receive Connectors.
Exchange maximum message size - Receive Connector
The Exchange Management Shell command for setting Receive Connector message size limits is very similar to the send connector command.
Set-ReceiveConnector "Default MAIL" -MaxMessageSize 50MB
Individual User Mailboxes ^
Finally as an Exchange administrator you are able to set Messages Size restrictions for both the inbound and outbound. I don’t generally set these unless I’ve got a problem user. Good example is the ever present user who gets regular e-mails with 20 unresized pictures of his/her grandkids. For this reason if you get complaints from a user you may want to check here to see if something is set.
This setting is set in the Mailbox properties, on the Mail Flow Settings tab, under Message Size Restrictions. You’ll have to check the box for each direction if you want to change the setting.
Exchange mailbox message size restrictions
For each mailbox you would like to change via the EMS you simply need to enter the following command.
Set-Mailbox –Identity “John Smith” –MaxSendSize 10mb –MaxReceiveSize 10mb
Order of Precedence ^
So how are these applied? Generally where the message first hits a limit is where the size restriction will take place. For example on an inbound message the Receive connector is applied first, if it passes it will then check the user’s mailbox for restrictions. In all cases, either inbound or outbound, the user mailbox setting trumps everything.
Spam Filter (optional) ^
As a final gotcha in trouble shooting this type of issue, you may want to check your external spam filter if you have one to make sure it doesn't have this type of setting and it isn’t too low. I personally use a Barracuda Spam & Virus Firewall 300Vx and by default it will allow up to 100 MB messages, but this may vary depending on your vendor.
Barracuda Spam & Virus Firewall 300Vx