Undelivered Mail Returned to Sender

[2ksales]

Can anybody tell me why I have started getting my emails returned?

This is the mail system at host relay3-d.mail.gandi.net.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

                   The mail system

[SKaero]

You would have to include more of the email message which should have more information of the failure. One thing to note this isn't a Roundcube problem is a mail server problem.