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.
