Maybe
VFE MAIL might be a strong candidate or the chart.
VFE mail offers free & paid versions.
FREE VERSION
WebMail or use with your e mail client.
IMAP
POP
SMTP
Encrypted(HTTPS/POP/IMAP/SMTP SSL)
Message box encryption
Virus Scanning
Spam Protection
Horde5 (default)
Horde (old)
Roundcube
PAID VERSION
In addition to the free version.
Extras,including aliases,more,storage/bandwidth quota, etc.
One special feature is called "Metadata Mitigator" which encrypts the metadata.