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 <jan.niklas.zimmerman(a)gmail.com&gt;: host gmail-smtp-in.l.google.com[173.194.69.26] said: 550-5.1.1 The email account that you tried to reach does not exist. Please try 550-5.1.1 double-checking the recipient's email address for typos or 550-5.1.1 unnecessary spaces. Learn more at 550 5.1.1 https://support.google.com/mail/?p=NoSuchUser 34si101268edi.496 - gsmtp (in reply to RCPT TO command)