While all ISPs score a sender’s reputation by giving different weight to various factors you can be assured that all major ISPs are using some type of equation to determine your reputation.   How they calculate your sender reputation score determines whether your mailing is received in the inbox, the junk mail folder, or even delivered at all.

Email Filters
Its important to familiarize yourself with the following individual filtering methods.  In the past ISPs would block emails based solely on one of these filters but as weaknesses in this approach became inherent they can no longer rely on any one method.  Each of the following filtering methods play a role in your ISPs’ delivery decision:

  • Content Filtering – Uses the email subject line and the body content to come up with a spam count score.  One of the most popular spam filtering packages is SpamAssassin which is used in EmailCheck.
  • List Quality Filtering – A lot of spam lists particularly paid subscriber lists contain a lot of bogus email which results in high bounce rates.   ISPs use this to detect which lists contain bounces that exceed a certain quantity and then disallow all emails from this IP address or sending domain.
  • Volume Filtering – Because spammers send bulk emails without regard to accuracy or volume this checks the number of simultaneous connections that are opened (known as threads) at any one time with your ISP.  The server may then reject all messages based on the number of open connections.  1-2-All Email Marketing uses a single thread sending method.
  • IP Address Filtering – When an IP address is added to this filtering list the process is known as “blacklisting.”   Once blacklisted all emails from a particular IP address are disallowed.
  • Domain and URL Filtering – Checks the email domain used to send a mailing as well as any URLs included in the message.

Legal Compliance
You need to be aware of regional laws aimed at curbing spam.   In order to ensure that your mailings are permission based it is good policy to ensure that an opt-in mechanism is in place before you begin email marketing.
Can Spam Act

  • ensure that all mailings contain a functional unsubscribe mechanism
  • all unsubscribe requests must be honored within 10 days
  • commercial mailings must include the physical location of the sender
  • criminal charges for fraudulent sender or deceptive subject lines

European Union E-Privacy Directive
Australia Spam Act of 2003
Whitelisting and Feedback Loops

Some ISPs provide whitelisting and compaint feedback loops as methods for improving deliverability.  Those that do typically require senders to have explicit opt in permissions for subscribers.

  • Whitelists -The opposite of a blacklist where the ISP receives requests from legitimate companies to be added to a list of pre-authorized e-mail addresses from which mailings can be delivered regardless of spam filters
  • Feedback Loops – A reporting mechanism whereby an ISP provides the sender with data including unsubscribes and spam complaints.

Spam Complaints
Most people have seen a “Report Spam” button on their email client.   When this is clicked on a spam complaint is logged at the ISP level or it is also relayed back to the sender if they are a part of a feedback loop.  If you receive too many spam complaints then you will damage your sender reputation.   A good way to reduce your spam complaints is to ensure that all of your subscribers are opt-in.
Spam complaints do not track the reason why recipients make a spam complaint.   It is possible that even if subscribers opt-in to your list they may forget they are subscribed or no longer find your mailing relevant.  If you receive a high number of spam complaints on a list where your subscribers have opt-in to then this is usually a good indicator that your mailings are either irrelevant or sent to frequently.