Customers migrating from native applications to Boxer may discover that large attachments may fail to download in Boxer or Inbox, despite being able to successfully download them in the native e-mail client.
- When attempting to download an attachment above a certain size, Boxer will report that the attachment is too large.
- The MaxAttachmentSize provisioning policy is set to allow an attachment of that size to download.
- Examining network traffic will reveal that the request to download the attachment (an ItemOperations ActiveSync command) returns a status of 11, indicating that the attachment is too large.
- The native iOS Mail application may still succeed in downloading mail.
The root cause of this is that the IIS setting for MaxDocumentDataSize is configured lower than the size of those attachments. This setting is independent from the MaxAttachmentSize provisioning policy, and should ideally be set to at least the size configured for that policy.
iOS Mail receives the same error, but also implements a fallback operation using the Sync command (which is not subject to the MaxDocumentDataSize setting) to fetch the entire MIME-encoded message. It can then parse the attachment from the MIME-encoded message.
This works, but has serious drawbacks in terms of bandwidth usage. First, the MIME-encoded message could include multiple attachments - end-users might need just a single small attachment, but will have to also download other attachments in the message, which could be quite large. Second, because the attachment will be download in MIME-encoded format, it will have a 10-15% encoding overhead as well.
- Customers experiencing this issue should configure their MaxDocumentDataSize and maxRequestLength settings as described in the following link:
- Office 365 tenants have a fixed limit of 25MB for these settings, as described here:
https://technet.microsoft.com/en-us/library/exchange-online-limits.aspx - BKMK_ExchangeActiveSync_Limits
- Future versions of VMware Boxer may implement the same fallback operation as iOS Mail. It is still recommended that customers implement the configuration changes above for significant bandwith savings.
Support Contact Information
The AirWatch Team