Message hash algorithm MTA option

Message archiving and hashing options:  (hash algorithm name)
The  MTA option controls what hash algorithm the MTA uses to generate a hash over the message. The value should be a hash algorithm supported by the MTA, one of MD2, MD4, MD5, SHA1, SHA256, SHA512, MD128, or MD160. The default is MD5.

See also:
 * Message archival and hashing MTA options