Abstract A storage-based anti-virus access gateway is not scalable because it stores the entire mail under processing. This work designs and evaluates a stream-based mail proxy constructed from several open-source packages. This proxy processes mail in segments, and interleaves MIME parsing, decoding, decompressing and virus scanning. It is seven times faster than the storage-based one on forwarding, three times faster on virus scanning, and twice as faster on decompressing plus virus scanning. This proxy can keep nearly constant memory usage and work without disks, while the storage-based one requires memory and disk space proportional to the number of clients and the mail size.