Our community theatre group has an online web sales facility, which dispatches PDF tickets to purchasers, which is stable and reliable, but, emails, or at least some emails, perhaps all, but the customer hasn't phoned up yet, to Xtra are not getting through to the customer, being blocked at the border.

<customer.email@xtra.co.nz>: host mx.xtra.co.nz[210.55.143.33] said:
    554-5.7.1 Message rejected due to possible spam content 554
    [664A93BD-78A1054A@mta2305] (in reply to end of DATA command)

If I copy and paste the email content (including attachment) into another email address on the same sending domain, then the mail is received by the customer.

Is there someone at Xtra I can contact to have our ticket sending email address whitelisted???