I have an exim4 server that forwards all input emails to a gmail account.
Gmail is refusing some valid messages with this error:
SMTP error from remote mail server after end of data: 550-5.7.1 Our system has detected that this message is likely unsolicited mail. To reduce the amount of spam sent to Gmail,this message has been blocked. Please visit https://support.google.com/mail/?p=UnsolicitedMessageError for more information.
I guess one of the problem is that my server is forwarding all messages, spam too. I have read this articlet from google support:
https://support.google.com/mail/answer/175365?hl=en
Seems that I have to be sure to not change the envelope, but how can I understand if my exim4 server is changing it?