Attachment Link on Size Policies

Document created by user.oxriBaJeN4 Employee on Sep 11, 2015Last modified by user.oxriBaJeN4 Employee on Jun 15, 2017
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Attachment Link on Size policies (also known as Strip and Link policies) allows administrators to specify an attachment size limit on inbound and outbound messages. However rather than denying the recipient access to the attachment, they receive the original email with a notification. The notification contains a link allowing them to download the attachments. This link is valid as long as the message is in your archive (e.g. your maximum retention period).


All emails triggering this policy will be logged in the Stripped Attachments viewer. This allows the administrator to release the attachment, or the full original email (including the attachment) to the intended recipient.


Both the Email Size Limits and Attachment Block on Size policies can overrule this policy. Additionally transmission encoding can considerably add to the overall email size, typically up to 35% and maybe as high as 50% depending on the number of attachments. Mimecast recommends increasing the threshold of the Email Size Limits Policy and the Attachment Block on Size policy to allow the attachment to be accepted and replaced with a download link.

Users with the relevant capability enabled, can choose to strip and link attachments over 1MB in size when using Mimecast for Outlook.



The Attachment Link on Size Policy allows Administrators to manage bandwidth and storage challenges, while still keeping up with end user needs. The recipient still have access to the email and attachments, without the attachments being delivered to the internal mail server. These are instead downloaded directly using the link provided.


The policy triggers on the combined binary size of all the email attachments. The binary size is the true size of an email component, excluding any form of encoding required by the mail server to transfer the component via SMTP. When handling archives (e.g. .zip) the configured threshold applies to the uncompressed file size. This provides protection against large, highly compressed archives.


For example, if the policy is set to 10MB, an email with 5 attachments with a cumulative size of over 10MB, will all be linked. This can assist with getting large attachments to external recipients.


What You'll Need


  • An Administrator Console logon with access to the Administration Gateway | Policies menu item.


Creating a Policy


To create a policy, follow the instructions in the Creating / Changing a Policy article, but using the following options:


Policy NarrativeProvide a description for the Policy to allow you to easily identify it in the future.
Link Attachments Larger Than (KB)

Specify a value in Kilobytes for the maximum file size of all attachments in a message. Any attachments that exceed this limit are placed not delivered with the message. instead the recipient is sent a notification, allowing them to download the file. For example if 1000 KB is specified and a message has two attachments of 550 KB each, both attachments are replaced with links.

Attachments under 50 KB in size are automatically ignored.


Definition Required?



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