Tags: Technical

Spam is something most people think of as an inbox problem – one that requires filtering inbound email traffic. Outbound anti- spam, however, is unwanted email sent to the Internet from an internal host or trusted user. It’s different from inbound spam in a few ways – most importantly, in how you control it. Outbound spam needs to be controlled to avoid the risk of blocking legitimate emails being sent from your network, due to IP blacklisting.

Inbound vs. outbound spam control

Simply reversing an inbound spam filter to cover outgoing SMTP traffic is not a workable solution for web hosts and other businesses that depend on getting email delivered. You need outbound spam filtering technology to stop spam from leaving your network before it causes your IP address to be blocked by anti-spam systems.

Outbound anti-spam filtering is a proactive solution that prevents your IP reputation from being damaged. It gives you insight into your email traffic stream and allows you to monitor your sending network so users or customers have secure access to reliable email delivery.

In both solutions, spam filters analyze messages and assess sender behavior to limit the amount of spam that makes it through the system. Yet there are two main differences between inbound and outbound spam control:

  1. Sender ID – inbound spam controls typically identify the sender using its IP address. For outbound spam control, the sender is your own customer or user; senders are identified by the account name, email address, or in some cases their internal IP address.
  2. Impact of false positives – when an inbound spam filter makes a mistake, one of your own users fails to receive a message. With outbound spam control, the false positive means someone else’s recipient fails to get the message - or potentially thousands of messages if it’s part of a legitimate bulk email campaign.

Managing and tracking sender identity in an inbound spam control system is relatively easy, because IP addresses are nearly impossible to falsify (in the context of SMTP email). Doing the same for outbound email, where the sender identities are more varied and more likely to be compromised or spoofed, is much more difficult.

But the impact of false positives is the greatest differentiator between inbound and outbound spam control. There is a huge difference between blocking, say, a particular newsletter from reaching one of your users, versus blocking EVERY newsletter sent out by one of your users to his or her mailing list of 1,000 recipients. With outbound spam control, mistakes can be much more costly than with inbound spam control.

The benefits of outbound spam filtering

Outbound spam filtering stops spam at the source. Think of it as “leak prevention” for your network – the automatic inspection of outgoing emails to remove spam and computer viruses before they’re sent out over the Internet.

You can set up outbound spam filtering to take place in a mail server, a transparent SMTP proxy within a network, or as a hosted email relay service.

The filtering technology streamlines, automates, and manages the abuse of email accounts and mail servers by spammers. It protects your network and helps you spend more time growing your business by spending less time reacting to the fraudulent signups.

Use outbound anti-spam filtering to eliminate the risk of blacklisting by analyzing email from all your servers to identify and isolate compromised accounts – before spam is sent.

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