unable to send email - 550 #5.1.0 Address rejected.

unable to send email - 550 #5.1.0 Address rejected.

Hi,

I've read through similar posts and checked that the MX records have been set-up properly see below, but still unable to send email to new domain.

output from nslookup
lightxcel.comINMX
preference:10
exchange:mx.zohomail.com
1800s(30m)
lightxcel.comINMX
preference:20
exchange:mx2.zohomail.com
1800s(30m)
Anything obvious I missed out.

Thanks