smtp-0b7e1e02ba8c6d7ce.core1.sfdc-urlt2q.mta.salesforce.com IXFR zone transfer

Changes since SOA version

IXFR is a zone transfer request that returns changes since a specific SOA version. Enter the SOA version to request changes since then.

Not an apex domain The domain smtp-0b7e1e02ba8c6d7ce.core1.sfdc-urlt2q.mta.salesforce.com is not the root of its zone.
Instead, try zone transfer on sfdc-urlt2q.mta.salesforce.com .