On 8/02/2017, at 1:24 PM, Peter Lambrechtsen <peter@crypt.nz> wrote:

The xtra.co.nz domain doesn't seem to have a DKIM or SPF record attached to it, in fact there isn't any txt record on the domain.

This isn��t a case of an SPF on xtra.co.nz but SPFs from senders that end up with final delivery being an Xtra mailbox.

<xxxxxxxxxx@xtra.co.nz> (expanded from <admin@yyyyyyyyyy.nz>): host
mx.xtra.co.nz[210.55.143.33] said: 550 5.7.1 Message rejected due to SPF
policy (in reply to end of DATA command)

where senders domain has -all on its SPF record.