cant esend email to external domains

A customer using mail1 cl2 can only send emails to other addresses on the same domain as their domain. Emails to external domains don’t arrive.
No problem with incoming mail just when sending, no bounces no nothing. I’ve set up a test account for that domain and experience the same behaviour from my location.

Anyone else on this mail server experiencing issues

Can you please check now and let us know the result?

I’ve responded to the ticket, all test mail is now coming through