Spam filters evaluate every incoming message and decide how to classify it. The widespread idea that it is enough to avoid certain words is an oversimplification – today it is above all sender reputation and recipient behaviour that decide, that is, whether recipients open messages, reply to them, or delete them unread. Content signals play a smaller but still present role: an unbalanced ratio of images to text, shortened links from unknown services, excessive formatting, lots of exclamation marks and capital letters, or a mismatch between the displayed and actual sender. Before sending a larger campaign, it is worth testing the message with a tool that scores it, and sending it first to test mailboxes at the main providers. It also helps to send from a domain with a longer history and not to change the sending address with every campaign.
See also: Sender reputation, Email rendering testing, Email subject line and preheader.
