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How does MailChannels Outbound Filtering work?

The Short Answer

MailChannels Outbound Filtering is an SMTP relay service that identifies spammers within your network to improve your email reputation and ensure reliable email delivery for your users. With MailChannels Outbound Filtering, you can eliminate email delivery problems caused by IP address blocklisting. You can also automatically shut down compromised end-user accounts and scripts to improve your security. Unlike conventional email delivery services, MailChannels Outbound Filtering is the only service that accepts 100% of your email, including spam.

The Long Answer

MailChannels Outbound Filtering is designed to relieve businesses of the cost and complexity of managing IP blocklisting and outbound spam. Our system works somewhat like a credit score, creating a reputation to determine the potential risk posed by an individual sender within a network. The sender could be an email user, an application like WordPress or Joomla, or a contact form.

Compromised Account Detection

Spammers are constantly searching for new resources from which to send their email. They partner with cybercriminals who exploit vulnerabilities in web applications and servers, and who compromise end-user accounts through phishing attacks and malware. The variety of ways in which spammers obtain resources is endless and constantly changing, and preventing their advance is nearly hopeless. While it’s definitely helpful to keep software up to date and to follow best practices for maintaining site security, outbound email processing and filtering is necessary in order to stay one step ahead of the spammers.

Because it’s not practically possible to stop spammers from exploiting your resources, you need to identify spammers by watching the email they generate. MailChannels Outbound Filtering uses sophisticated algorithms and machine learning approaches to spot spam-like trends in the stream of outgoing email coming from your servers and applications. Additionally, MailChannels Outbound Filtering pinpoints the sending entity (whether it be a user, application, or server). When a flow of email traffic begins to look suspiciously “spammy,” MailChannels Outbound Filtering shuts it down and generates an informative notification that you can process either via an API webhook, or a human-readable email message to take action against the spammer.

Here are some of the techniques used by MailChannels Outbound Filtering to identify resources that have been compromised by spammers:

  • MailChannels Outbound Filtering uses digital signature technology, checking the content of each email message against a real-time updated database of known spam signatures. A sudden uptick of spam messages identified in this way may trigger rate-limiting or blocking of a sender.
  • MailChannels Outbound Filtering tracks dozens of minute-by-minute statistics about each email sender. Unusual trends in message volume, suspicious content, recipient validation failures, and other statistical signals enable identification of spammers.
  • MailChannels Outbound Filtering consults external databases such as domain and IP reputation services to identify email messages relating to known spammers.
  • MailChannels Outbound Filtering analyzes responses from email receivers to gauge whether receivers like the email being sent by your users, applications, and scripts. Based on this feedback, spammers can be identified even before other signals indicate a problem.


When MailChannels Outbound Filtering identifies a spammer within your network, it sends you a notification so that you can proactively remove the spammer - for example, by disabling a user account or a WordPress plugin that has been compromised. Notifications are sent either via human-readable email, or using a webhook, which enables you to shut down compromised accounts in seconds.

Multi-Password Support

MailChannels Outbound Filtering lets you create multiple passwords for SMTP authentication with the service. You can use a different password with each of your servers and retire old passwords with a single click if you need to shut down access because of a compromise or breach.

Multi-User Support

MailChannels Outbound Filtering lets you create unlimited web console logins for your staff. Select between regular and administrator access levels to provide appropriate access to technical staff and administrative staff. 

Email Management Features

Log Search

MailChannels Outbound Filtering logs every email delivery attempt made by your users, showing you what happened in case there’s a problem. Search through months of logs in seconds via an intuitive web interface to quickly answer questions about email delivery.


MailChannels Outbound Filtering provides easy-to-understand non-delivery reports (NDRs) when email is rejected, helping users resolve their own delivery challenges. A link provided in each NDR takes the user to an “Insights” page where they review all of the email sent from their address. Insights reduces the amount of work you have to do as a service provider by helping users help themselves instead of calling your support desk.


If you haven't already, sign up for MailChannels Outbound Filtering.

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