Shieldwall Listings – Why Am I Getting ‘421 Too Many Recipients’?

Securence places sensible limits on all outbound mail delivery through its SMTP servers. If your outbound mail volume significantly increases in a short period of time, this may trigger a block by Securence’s Shieldwall engine. This is designed to protect compromised machines and compromised user accounts from sending unsolicited messages using your assigned IP address, tarnishing its reputation and causing further issues. If you are having difficulty sending outgoing mail through Securence because of a 421 Too many recipients error, this indicates your IP has been listed by Shieldwall. Shieldwall listings are temporary and as soon as your mail volume returns to normal levels your IP will be automatically removed from the block list.

What should I do if my IP becomes listed on Shieldwall?

  1. Identify what has caused the large increase in your outbound mail volume. This can be easily accomplished by logging into and checking the Reports and Mail Log sections. The most common issues are:
    • Company newsletter
    • Compromised/infected machine on your network
  2. Depending on the source of the problem, you may need to change the password of a user on your network to stop the flow of spam/viruses. Either way, if there are a large number of messages queued on your server that should not be delivered, these messages must be deleted. Otherwise, it will take a lot longer for the Shieldwall listing to get removed.
  3. Wait. (We know, that’s the hard part. But it won’t take long, we promise!)  If you have identified the problem, and removed the messages from your server, the Shieldwall listing will be automatically removed in about an hour.