Proxy hash algorithm MTA option

XPEHLO proxy validation:  (hash algorithm name)
New in MS 8.1.0.3. The  MTA option controls what hash algorithm the MTA uses to authenticate the contents of an XPEHLO command. The value should be a hash algorithm supported by the MTA, one of MD2, MD4, MD5, SHA1, SHA256, SHA512, MD128, or MD160. MD5 is the default. Note that the setting of this option must be the same across a deployment for successful operation of the XPEHLO command.

See also:
 * Memcache MTA options