Enable the Bypass internal domain urls option. This will allow ScanMail to bypass messages containing internal domain URLs, which will reduce network bandwidth usage and reduce the Virtual Analyzer working load if URL Analysis is enabled

Add your company’s internal URL to the "Approved URL List". This will allow ScanMail to bypass messages containing internal URLs, which will reduce network bandwidth usage and improve performance.

Use a Smart Protection Server to reduce network bandwidth usage. Web reputation services sends URL queries to the external Smart Protection Network or to the local Smart Protection Server. Networks can suffer a performance impact with a slow Internet connection when querying the Smart Protection Network. Configure a Smart Protection Server using the management console and change the web reputation source by clicking Smart Protection → Scan Service Settings.

To optimize Smart Protection Server performance, consider a dedicated Smart Protection Server for ScanMail. If your Smart Protection Server is providing services to both ScanMail and Appex One, for example, server performance could suffer.

Scanning attachments for URLs can introduce a performance impact to your system. If you are already using content filtering or Data Loss Prevention policies with attachment scanning, the URL scanning in attachments should introduce a limited impact to your system. If you are not using content filtering or Data Loss Prevention policies with attachment scanning, using the URL scanning in attachments can noticeably affect performance.