“Mailbox Quota Exceeded” when sending large attachment 7.5 MB and above with Blackberry Work

Nowadays, we have several choices when it comes to file sharing (i.e. Box, Google Docs, SFTP, etc.) But old habits die hard and unless your organization operates IT like Fort Knox, chances are your users will often share files via email anyway from time to time. Recently, my service desk team brought to my attention that iOS users receive the error below when emailing large attachment around 7.5 MB and above with Blackberry Work.


Interestingly, I also discovered similar errors when emailing from a device configured with native Exchange ActiveSync in the mail profile.

largeattachmentwithBlackberryWork2.jpg     largeattachmentwithBlackberryWork3.jpg

Based on the above, this issue most likely caused by a setting somewhere in the Exchange policy especially since I already checked and confirmed that user’s mailbox has yet to exceed any quota. Below are the steps I took to investigate and resolve this issue in my environment.

If you use any sort of email gateway appliance, you may want to check and see if you have any limit set there for outbound mail/attachment as well before proceeding further below.

First of all, we need to check app configuration within Blackberry Work to ensure it is set above the default value of 10 MB. Specifically, this setting is under the Docs and Attachments tab for both cloud-based and on-premise customers.







During my investigation, I came across the links below which ultimately help resolve this issue.

Spoiler alert: the fix (at least for me) is to adjust the maxRequestLength from the default (10 MB) to say 30 MB on every Exchange server. Then reset IIS for the change to take effect immediately.

Specifically, the value is found within the web.config file located at:

  • On Client Access Server: %ExchangeInstallPath%FrontEnd\HttpProxy\Sync\web.config
  • On Mailbox Server: %ExchangeInstallPath%ClientAccess\Sync\web.config


There are two things to keep in mind when modifying this value:

  • To allow for a 33% increase in size due to Base64 encoding, multiply your desired new maximum size value in megabytes by 4/3. To convert the value into kilobytes, multiply by 1024. To convert the value into bytes, multiply by 1048756 (1024*1024). Note that the size increase caused by Base64 encoding could be greater than 33%, and depends on several factors, for example, the attachment file size, type, compression, and the email client used to compose and send the message.
  • Any customized per-server settings you make in Exchange XML application configuration files, for example, web.config files on Client Access servers or the EdgeTransport.exe.config file on Mailbox servers will be overwritten when you install an Exchange Cumulative Update (CU). Make sure that you save this information so you can easily re-configure your server after the install. You must re-configure these settings after you install an Exchange CU.

Before taking the steps above, I also came across this post by running the below. However, it doesn’t resolve the issue.

set-transportconfig -ExternalDsnMaxMessageAttachSize xxxMB

I hope you find this post helpful. As always, stay mobile!

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