I have an interesting one here....
Sending an email to a domain that seems to use Gmail spam protection is being blocked on a 550 5.7.1
However, checking all RBL lists, making sure that SPF / DKIM all is aligned and everything looks OK. I have confirmed all passes using UnlockTheInbox, 'http://dkimvalidator.com' and allaboutspam.com.
I sent a test plain text email to the recipient and that still bounced:
Could not deliver message to the following recipient(s):
Reason: Remote host said: 550 5.7.1 [18.104.22.168 12] Our system has detected that this message is
5.7.1 likely unsolicited mail. To reduce the amount of spam sent to Gmail,
5.7.1 this message has been blocked. Please visit
5.7.1 more information. f7si9048319wix.75 - gsmtp
IP Address stated is our main mail server outgoing IP.
Has anyone seen any changes as this was working fine!