Receiving “Mail delivery failed: returning message to sender” messages on virtually ALL emails being sent to @hotmail, @outlook, @live, and @yahoo servers.
What types of modifications can I make to the message or the config file to help these servers not flag my emails as spam?
Here is the entire message:
This message was created automatically by mail delivery software.
A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:
host hotmail-com.olc.protection.outlook.com [IP ADDRESS]
SMTP error from remote mail server after RCPT TO:<[SENTTOADDRESS@hotmail.com]>:
550 5.5.0 Requested action not taken: mailbox unavailable (S2017062302).
Any and all suggestions welcome.