How to prevent your emails from being marked as spam. You want to prevent your emails going to a recipient's Spam or Junk folder.
Most ISPs filter all incoming email against a spam filter, which grades the content of each email with a spam score. The higher the score, the higher the likelihood that the email is spam. If an email score exceeds 5 points, it is blocked or delivered to the recipient's spam folder.
Administrators should test email campaigns participant emails, by sending a small test to Yahoo and Hotmail email accounts. The admin should maintain a free account on those systems for testing.
After sending the test email, check the spam score by reviewing the full email headers. The spam score should be less than 5.
How to Find Email Headers
GMAIL: To view message headers in Gmail, click the down arrow next to Reply, at the top-right of the message pane. Select Show original.
YAHOO: To view message headers in Yahoo, click the Full Headers in the lower-right corner of the page.
HOTMAIL: To view message headers in Hotmail, right-click on the message in the Message list and choose "View source." If you are using the classic version of Windows Live Hotmail, this feature is not available.
What follows is an example header section that shows a score of 5.480. Since this is greater than 5, it is being marked as spam:
X-Spam-Status: Yes, hits=5.4 required=5.0
tests=AWL: 0.479,MISSING_MID: 0.001,RDNS_NONE: 0,
CUSTOM_RULE_SUBJECT: 5.00,TOTAL_SCORE: 5.480,autolearn=ham
Please note this item: CUSTOM_RULE_SUBJECT: 5.00
In this example, the administrator used a combination of certain words (i.e. 'fundraising') in the subject of the email that triggered a spam rule and raised the spam score. By changing the subject and re-sending, the administrator can lower the spam score to under 5 points, and the message will not read as SPAM when it's delivered.
We know that it is frustrating to have your carefully constructed emails marked as spam! However, we have no control over this as it is an externally marked filter. When this happens, you will need to test alternative subject lines until the mail is properly received. You are welcome to send your tests to email@example.com, firstname.lastname@example.org or email@example.com so we can review your spam scores with you.
Some email providers use Sender Policy Framework (SPF) to detect spam. Yahoo uses SPF and recognized our email server as a permitted sender, and no spam checking is performed.
Sender Policy Framework (SPF) is an email validation system designed to prevent email spam by detecting email spoofing, a common vulnerability, by verifying sender IP addresses. SPF allows administrators to specify which hosts are allowed to send mail from a given domain by creating a specific SPF record (or TXT record) in the Domain Name System (DNS). Mail exchangers use the DNS to check that mail from a given domain is being sent by a host sanctioned by that domain's administrators
You may which to send emails to other email addresses as well, to check the spam score. Those that do not use SPF will normally provide the spam score as above.
For more, see this helpful article on how to test your Email campaign against spam filters.