This is the mail system at host mail.zapf.in. 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 <mark718holmes(a)gmail.com&gt;: host alt1.gmail-smtp-in.l.google.com[142.250.153.26] said: 450-4.2.1 The user you are trying to contact is receiving mail at a rate that 450-4.2.1 prevents additional messages from being delivered. Please resend your 450-4.2.1 message at a later time. If the user is able to receive mail at that 450-4.2.1 time, your message will be delivered. For more information, go to 450 4.2.1 https://support.google.com/mail/?p=ReceivingRate z25-20020a170906715900b00a1c2b253e9asi1351700ejj.7 - gsmtp (in reply to RCPT TO command)