Forwarding to Gmail blocked

Hey,

I've been forwarding a mail with important travel details to my partner and my family, who (still) use Gmail. However, the mail never arrived. I got this error

Undelivered Mail Returned to Sender This is the mail system at host mail.w14.tutanota.de.

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

xxx@gmail.com: host gmail-smtp-in.l.google.com[64.233.167.26] said: 550-5.7.1 [185.205.69.214 12] Gmail has detected that this message is 550-5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail, 550-5.7.1 this message has been blocked. For more information, go to 550 5.7.1 https://support.google.com/mail/?p=UnsolicitedMessageError ffacd0b85a97d-3e7609117a3si616294f8f.702 - gsmtp (in reply to end of DATA command)

Help would be much appreciated.