Mail Poet Sending Service not sending

I’m sending with the Mail Poet service. The email list shows 221/221 sent, 0 opened 0 clicked. I’ve phone checked a dozen recipients – no-one has received an email yet. Our usual open rate is 30% in 15 minutes. This time no results after 45 minutes. MailPoet Free version: 3.54.0 MailPoet Premium version: 3.54.0