Artem Abgarian, the Semalt Senior Customer Success Manager, says that spam filters can frustrate marketers even if they have permissions and notarized documents signed by the end users. Practice when legitimate email messages get marked as spam is called "false positive." In the most cases, such situation occurs when recipients do not use the major ISPs like Yahoo, Google, Hotmail, and AOL.
Major ISPs have tailored their spam filters towards user experience while smaller businesses use commercial spam filters. Commercial spam filters work on three levels of defense: filtering emails before they reach the server, filtering emails after they reached the server and finally filtering mails on the user's desktop.
These filters scan mail content to detect spam. After your message gets to the filter, it is evaluated regarding these criteria: words and phrases, image size, links, etc. In this regard, it is obvious that marketers need to know words and phrases that trigger spam filters and try to avoid them. Most developers of email filters do not share this information, and their filters keep changing to respond to the current spam trends. However, providers like Spam Assassin disclose a bit of helpful information that can come in handy if you don't want your messages to be categorized as spam. Email filters are being improved all the time to ensure spam does not get to the inbox.
Some businesses use filters that focus on headers and the sender's reputation. They study how many recipients marked your mail as spam. Other filters try to find out if the emails sent to employees are work-related or not. An email that fails the test is sent to junk.
Some filters rely solely on the end users. If users accept your mail in their inbox, you can keep sending them mail without worrying about spam filters. In such case, obtaining the permission of the end users prevents spam filters from sending your mail to the spam folder.
Tips on how to avoid being marked as spam:
Avoid all image emails
Emails with images look more attractive, but not to spam filters. Quite the opposite, in fact, spam filters perceive such messages as suspicious ones. So, always review your images to text ratio, because improper text can send your email to spam.
Keep off spammy words symbols, and punctuations
Words like sex, free, offer, call now, Viagra and 'buy now' activate spam filters pretty quick.
Use capital letters sparingly
Lots of capital letters on your subject line can trigger filters to categorize your mail as spam. Also, keep the subject line concise and straightforward.
Attachments are often used for nefarious purposes, so a mail with attachments has higher chances to be marked as spam by filters. This is also because some filters cannot scan attachments for malicious files.
Finally, avoid sending links that lead readers to a page containing nothing except images. Let links lead to legitimate landing pages with text. To avoid troubles, remember to send mail only to those who have subscribed to your list.