Incoming E-Mails with Excel attachments are not delivered
Description
This article explains why some E-Mails with Excel files in attachments are being blocked by Gateway Antivirus even if they don't contain macros.
Cause
Gateway Antivirus recognizes the Excel files in *.xlsx format as multiple level compressed zip/gzip files, blocks them and generates the following Log Message:
AV Gateway Alert - Gateway Anti-Virus Alert: Multi-compressed ZIP/GZIP file blocked
This occurs when the option "Block files with multiple levels of zip/gzip compression" is enabled in Global GAV Settings and it's caused by the the specifics of the XLSX format. Excel automatically compresses the *.xlsx file (using ZIP compression) when the file is saved and decompresses it when it's opened.
Resolution
In order to allow the *.xlsx files, blocking of multiple level compressed zip/gzip files needs to be deactivated:
- Login to the configuration page of the SonicWall.
- Navigate to Security Services | Gateway Anti-Virus.
- Click on Configure Gateway AV Settings button and deactivate the option "Block files with multiple levels of zip/gzip compression".
- Confirm by clicking OK and then Accept at the top of the page.