My coworkers first reaction was  hey, why are the sending limits so low, 5mb is nothing for an attachment size?

My first response was, we do not have 5mb attachment limits but have them to set to 30mb ……….

What to do?

I opened a trusty TS session to the CAS server that he was connected too and I knew that in the web.config file there is a setting that OWA uses to specify that max attachment size.

Note : By deafult the web.config file is located C:\Program Files\Microsoft\Exchange Server\V14\ClientAccess\Owa

After I opened the web.config file with notepad I located the section for <httpRuntime maxRequestLength=”30000″ />

The <httpRuntime maxRequestLength=”30000″ /> is stored in Kb which mean that OWA defaults to 30MB attachment size limits so that could not be that users problem

Where are all the attachment size limits?

1. trasnport config

2. Send connectors

3. recieve connectors

4. users mailbox settings

Lets open EMS and take a look…………

The first command we are going to run is get-mailbox Brian.Tirch | fl max*

we can see that current the user does not have any limits set for sending or receiving.

Next we check our send connector which by default is configured for a 10mb limit so that could not be it……

that does not appear to be the issue ….

Lets check the receive connector which by default is set to 10mb

we can see the connectors on each server are set to 10mb and should not be causing the issue…with only one place left to check and that is the transport configuration.

Lets use the get-transportconfig | fl max* command to get our settings

by default in Exchange 2010 this should be set to 10mb but in this situation you can see that we are set to Unlimited just like on our users properties.

After checking all the settings there is nothing configured to force OWA to a 5mb attachment limit so now what do you do………. After reaching out to some friends in MS who ran into this before we found out that unlimited on the transport config does not really mean no limit

The problem here is the meaning of Unlimited…  Basically Unlimited means that the values for the MaxSendSize and MaxMessageSize are not specified.  It doesn’t mean any size message will be sent. 

There are limits for mailbox, system, and connectors.  The MaxSendSize for the system is set with set-TransportConfig.  The MaxMessageSize for the ReceiveConnector and SendConnector are set on those connectors.  When the attributes for a user, “submissionContLength” and “deliverContLength” are not set in AD (default setting) a query by “get-TransportConfig” will return that the size is also unlimited.  However, the exact meaning is that the MaxSendSize is that the setting is not specified.
In this case, the sending code will use its own way to decide what is the maximum allowed send size.  If the client is OWA, the default maximum allowed message size is 5MB when the MaxSendSize is not specified.  If the MaxSendSize returns a value, OWA will use that value up to the value set on the maxRequestLength in the web.config.