This is the mail system at host mail.localdomain.
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
firstname.lastname@example.org: host gmail-smtp-in.l.google.com[188.8.131.52] said:
550-5.7.1 [220.xxx.xxx.48 7] Our system 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. Please visit
550-5.7.1 https://support.google.com/mail/?p=UnsolicitedMessageError 550
5.7.1 for more information. x61si13415410plb.328 - gsmtp (in reply to end
of DATA command)