An action by an ISP to not forward your email messages to the recipient. This is a distinct activity from a Bounce.
An action by an Internet Service Provider to prevent email messages from being forwarded to the end recipient.
A refusal by an ISP or mail server not to forward your email message to the recipient. Many ISPs block email from IP addresses or domains that have been reported to send spam or viruses or have content that violates email policy or spam filters.
Refusal by an ISP or mail server to allow your email message to go through to a recipient on the basis of suspected spam, viruses or violation of email policy. Also see Blacklist
A refusal by an ISP or mail server to forward your e-mail message to the recipient.