A user who sends email through Symantec Email Security.cloud receives a bounceback email indicating that the sending server's IP address has been blacklisted.
Common bounceback errors related to blacklisted IP addresses include:
I was unable to deliver your message to the following addresses
connect to domain.com: 550 Connection refused - we hate spammers!
host domain.com said: 554 Denied
host domain.com said: 552 spam source blocked
Note: These errors vary depending on the recipient's mail transfer agent (i.e. MTA, or mail server).
These errors indicate that Email Security.cloud attempted to deliver the message to the intended recipient’s server, but the message was rejected by the server, typically due to email blacklists.
IP addresses for Symantec.cloud may occassionly get blacklisted due to users who abuse the service by sending spam, or from compromised servers relaying spam through the Symantec.cloud email infrastructure.
Symantec proactively monitors email blacklists, and delivery problems associated with these errors are usually temporary.
To check if a specific Symantec.cloud IP address is in a blacklist, use the following 3rd-party services: