When leads fail to delivery, MetaLocator captures the bounce and stores an enumerated value along with the lead in the action field . The values are as follows:
BOUNCE_TRANSIENT: Amazon SES received a general bounce. You may be able to successfully retry sending to that recipient in the future.
BOUNCE_PERMANENT: Amazon SES received a permanent bounce. MetaLocator will remove the value in the location email field in this case and log the issue in the system log.
BOUNCE_UNDETERMINED: Amazon SES received a bounce, but the cause was undetermined. No action is taken by MetaLocator in this case.
These values come directly from Amazon as documented here.