This error message occurs when the delivery of an e-mail failed:
"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:
SMTP error from remote mail server after initial connection:
host smtp-fw-33001.domain.com [184.108.40.206]:
554 SBRS score too low: http://www.senderbase.org/ "
What does that mean?
The reputation (a value that determines whether emails of the server accepts or rejects) the mail transmission server is too low and therefore the e-mail was rejected. Therefore lands the sending server on a blacklist. Reasons for this may be that the sending client PC (tablet, mobile phone, etc.) is infected by a malicious program / Trojans or even the server itself.
What can you do?
One solution is to send the email on another account (aol.com, hotmail.com, gmail.com, etc). Also recommended is to scan your own PC for malicious software. If the problem occurs only when the e-mail sent over the first used an email account and the IP of the sending server is on the blacklist, then speak with the service provider. If the error is there, the problem is usually resolved within a day, because the rating of "SBRS" is dynamically updated.