You can enable real-time scanning of attachments in outgoing emails sent using the {product-short} Web Client. If enabled, when an attachment is added to an email, it is scanned using ClamAV prior to sending the message. If ClamAV detects a virus, it will block attaching the file to the message. By default, scanning is configured for a single node installation.
To enable using a single node:
zmprov mcf zimbraAttachmentsScanURL clam://localhost:3310/
zmprov mcf zimbraAttachmentsScanEnabled TRUE