EDIT: Before going through this blog, please note that there are other secure ways ( including sharefile ) to deliver large attachments. This blog’s primary goal is to showcase the large attachment delivery using WorxMail. Could be helpful if you don’t want to leverage other file sharing mechanisms and use only WorxMail to download/open/edit the documents.

As a part of Exchange ActiveSync limitations it has been observed that the maximum mail attachment size is 10MB (set as default on Exchange Active Sync).

This document describes in a step by step way how to overcome this limitation set by EAS server.

Note: The following document involves in modifying web.config file on Exchange server.

Use-Case:

1)      Compile and send a mail that has large attachment (more than 10MB) from <user1> to <user2>.

2)      Enroll and logon to WorxMail as <user2>.

3)      Download the attachment.

 NOTE: The following steps are only to demonstrate the capability of WorxMail to open large attachments, the changes on Exchange Server have to be analyzed by Exchange Admin before proceeding.

Step1: Compiling and sending a large attachment

Step NO

  
 1.           By default, OWA does not allow users to attach documents/files over 10MB.The following error is seen in that case:

2.          

To resolve this: goto Exchange Management Console.
3.          

Expand Microsoft Exchange On-Premises

  
4.           Go to Organization Configuration > Hub Transport

 
5.          

Click on Global Settings tab and open properties of Transport Settings.
6.          

Note that under General tab, Transport Limitsfor Receive and Send is of 10MB by default.
7.           Here is a detailed explanation of Transport Limits and Transport Dumpster settings before you edit. (Source: Microsoft)

Transport Limits and Transport Dumpster settings
Maximum receive size (KB) This field specifies the maximum message size that can be received by recipients in the organization. The default value is 10240 KB. The valid input range is from 0 through 2097151 KB. If you clear the check box next to Maximum receive size (KB), no limit is imposed on the message size that can be received by recipients in the organization.
Maximum send size (KB) This field specifies the maximum message size that can be sent by senders in the organization. The default value is 10240 KB. The valid input range is from 0 through 2097151 KB. If you clear the check box next to Maximum send size (KB), no limit is imposed on the message size that can be sent by senders in the organization.
Maximum number of recipients This field specifies the maximum number of recipients in a message. The default is 5000. The valid input range is from 0 through 2147483647. If you clear the check box next to Maximum number of recipients, no limit is imposed on the number of recipients in a message. Exchange 2010 treats an unexpanded distribution group as one recipient.
Maximum size per mailbox database (MB) This field specifies the maximum size of the transport dumpster for each mailbox database. The default value is 18 MB. The valid input range for this parameter is from 0 through 2097151 MB.
To enable the transport dumpster, the value of Maximum size per mailbox database (MB) must be greater than 0, and the value of Maximum retention time (days)must be greater than 0.
Maximum retention time (days) This field specifies how long an e-mail message should remain in the transport dumpster. The default value is 7 days. The valid input range is from 0 through 24855 days.
To enable the transport dumpster, the value of Maximum size per mailbox database (MB) must be greater than 0, and the value of Maximum retention time (days)must be greater than 0.
Specify the external postmaster address This field specifies the e-mail address used as the sender for system generated messages and notifications sent to senders external to your organization.
8.          

Edit the Maximum Send Size and Maximum Receive Size according to the organizational requirement.
9.           Open Services.msc
10.          Restart Microsoft Exchange Information Store Service.
11.          Wait till the service is restarted. 
12.          Now you should be able to attach the document in OWA to send it to the intended recipient.

Step 2: EAS configurations to be able to receive large attachments

Step NO

  
1.           Normally Exchange Active Sync is not configured to download attachments which are more than 10MB.We usually see the following error:
2.           To overcome this limitation: Go to : <Exchange Install Directory>\Microsoft\Exchange Server\V14\ClientAccess\SyncAnd duplicate Web.Config(as a backup).
3.           Edit Web.config
4.           Search for ‘maxRequestLength’
5.           Note that maxRequestLengthis 10MB by default.
6.           Change this to the required size (N X 1024)KB. Where N is the number of MBs you want.In the image changes are made to accept upto 25 MB.
7.           Search for maxDocumentDataSize.
8.           By default its 10 MB ( in bytes).
9.           Change it to required size.Changed it to 25MB in the image below.
10.          Go to Services.msc
11.          Restart Microsoft Exchange Information Store service.
12.          Wait till the service is restarted.
13.          Now the attachments are downloaded.
14.       
 		 The following table illustrated the sample payloads tested by making the changes described above on Android and iOS devices with only WorxMail and WorxEdit installed.Where NS = Not Supported; Y= Yes.The document is based on test results on internal setup. Kindly excuse typos. Feedback is appreciated.