How does the junk filter work?
When you send email, your recipient’s email server executes a quick handshake with the sending email server, taking note of your server’s IP address holding the email while it performs a quick reference check before allowing the message through. This reference check typically involves checking to see if your IP address is on a black list (or block list), checking if your email address is whitelisted by the ISP or the recipient, and checking the content against a set of rules to determine if it may be spam. Depending upon your recipients’ server set-up, some combination of these checks may cause your email to be blocked, put into the junk folder, or passed into the inbox.
A spam content filter looks at the content contained in the email message (words, html code and links) and filters out those with wording or html patterns that match known spam. The filter scores each message on a point system for each rule infraction, and the mail server administrator sets a threshold score for what is to be considered spam. Rules are added and modified over time, to keep up with the latest tricks and spam techniques.
The large ISP’s like Yahoo and Hotmail each maintain their own set of black list, white list and filter rules, which are somewhat different from those used on your corporate Exchange Server. This means there are no hard and fast rules for getting all your email through every time, yet the concepts are all the same, and the following advice will help legitimate senders reach in the inbox more often.
How do I avoid having my legitimate email put into the junk folder?
- Don’t use Bcc. This was one of the first methods spammers used, which means any email sent with a Bcc most often ends up in the junk folder. A primary benefit of PoliteMail for Outlook is its ability to send individual email messages to lists, without using the Bcc field.
- Avoid these words in your subject line. Avoid exclamation points!! *asterisks*, cash, congratulations, free, guarantee, mortgage, wealth and any action words which promote, such as “Act,” “Buy,” “Get,” “Order,” “Respond,” and “Save” especially when combined with “Now,” “Quickly” or “Today.” The content filters consider these to be “aggressive” and most likely spam.
- Don’t get clever with the subject line. You’ve probably experienced the feeling, when you open an unknown but innocent looking email and then think, oh, they tricked me. Remember that spam is in the eye of the beholder, so don’t write misleading subject lines just to get them opened. If you are sending commercial email, putting your brand name at the start of the subject line will help get you recognized. If you are sending a newsletter, start the subject with the name of the newsletter, then the topic. Try to keep your subject lines to about 50 to 60 characters, as that is all that will get displayed in the majority of email clients.
- Don’t send extra-large messages, an entire message as one image, or include large images. Many content filters also consider size when filtering out email. An average email is only about 10-40Kb in size, but placing images into your message can bloat the size to several hundred Kb or even megabytes. If you want to include pictures, its better to place them into your message by reference, that is, the image exists on an internet accessible web page, and the email can just display it by looking it up online, as opposed to the entire image being embedded into the message. PoliteMail’s Add Graphic Image command will automatically take care of this for you, keeping your message small.
- Be careful with attachments. Attachments, particularly executable files, are often used by spammers and may send your messages directly to the junk folder. Also, if you are sending large attachments or PDF files, the receiving mail server may reject your message (and may or may not tell you about it). The PoliteMail SmartAttachment™ feature will allow you to send PDFs and file attachments as links, keeping your email small and more likely to get delivered (with the side benefit of knowing when your recipient actually opens the file you sent).
- Don’t use the word “unsubscribe” or “remove me” in your opt-out footer. This is a surprising, but true, new rule. A better way to word your opt-out link message is “please take me off your list.”
- Test your message. It is a good idea to send your message to a test list of addresses from a number of domains (Yahoo, Gmail, Hotmail, etc.) using your own list or through PoliteMail’s Preflight Test Send feature.