Your message wasn't delivered to xxxxxx@gmail.com because the address couldn't be found, or is unable to receive mail.
(I am currently logged in to the gmail address it is telling me does not exist, and am sending the email from another gmail account.)
Email routed through SES is getting through though.
This is going to be a mess to clean up due to automated blocking of bounced addresses
Seems to be ongoing and blocking many (but not all) emails to accounts being reported as not existing.