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 reply-mx.s7.exacttarget.com is not the root of its zone.
Instead, try zone transfer on s7.exacttarget.com .
Instead, try zone transfer on s7.exacttarget.com .