> Source: [sk115935](https://support.checkpoint.com/results/sk/sk115935)

# sk115935 - Emails with large attachments fail to arrive when MS Exchange is configured behind SMB appliance and Anti-spam is turned on

| Property | Value |
|----------|-------|
| Solution ID | sk115935 |
| Date Created | 2017-02-19 |
| Last Modified | 2019-12-30 |
| Technical Level | Advanced |
| Products | Security Gateway, Spark Firewall (Locally Managed) |
| Versions | R82.10, R82, R81.20, R82.00.X, R81.10.X |
| Platform | 910 |

## Symptoms

- * Emails with large attachments fail to arrive to MS Exchange server that is configured behind the SMB appliance.
* Emails with no attachments, or with attachments smaller arrive successfully.
* If Anti-Spam blade is turned off the issue does not happen.
* If Anti-Spam is on and "scan email content" box is unchecked the issue does not happen.

## Cause

MS Exchange server is using BDAT (SMTP Command Protocol Extension) by default to receive and deliver large attachments.

Handling BDAT traffic when content based anti-spam is turned on requires more resources than handling DATA traffic, even without actually applying content based anti-spam inspection. The required resources depend on the size of the file and so large files easily exhaust the free resources before the email is successfully passed to the server, which prevents the emails from being sent.

Hence BDAT is currently not supported on SMB appliances when content based Anti-Spam is chosen, see [SK116115](https://supportcenter.checkpoint.com/supportcenter/portal?eventSubmit_doGoviewsolutiondetails=&solutionid=sk116115).

## Solution

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