sending a group email 5 with btinternet addresses were returned by mailerdaemon

[DavidTogneri]

mailer-daemon at

host mx-out.tt.xion.ocxs.net TO hostmk.bt.prod.cloud.openware.ai

ALL EMAILS TO btinternet addresses recd this rejection

Any comments anyone??

[kanya-TT]

Hey there, David. Is this happening when you send these emails via an client email app? 

Kanya