mtaStoredVolume

The total volume of messages currently stored in the MTA,
measured in kilo-octets.  This volume should include all
stored data that is logically above the mail transport
protocol level.  For example, an SMTP-based MTA should
use the number of kilo-octets in the message header and
body, while an X.400-based MTA would use the number of
kilo-octets of P2 data.  This includes messages that are
awaiting transmission to some other MTA or are waiting
for delivery to an end-user or application.

MIB

MTA-MIB

OID

.1.3.6.1.2.1.28.1.1.5

Type

column

Access

readonly

Status

current

Units

K-octets

Parent

mtaEntry