If the detection of a sending rate is too large and the inconsistencies in the identification of the sender have long represented the causes of the anti-spam filter triggers of the ISPs, they were complemented by a deep analysis of the content of the emails. To ensure the deliverability of an email campaign, the writing of messages respecting a precise technical form and quality proves to be paramount.
Spamming emails usually use commercial promised and a basic vocabulary. Therefore, anti-spam filters will notice emails with generic terms and words such as FREE. It´s important to avoid this and to always try to customize your fields to personalize your newsletter. Also, make sure to have a rich, coherent content with a good title.
To answer to the threat of malicious code, which infect the machine of the recipient, the anti-spam ISP now deals with the technical aspect of the message. The production of a clean and optimized HTML markup represents a first step to go through this filtering, that completes a transparent identification of the servers charged of the display of the different images of the graphic layout. Other prohibitive errors concern the "object" field of the emailing: it will be necessary to avoid leaving it empty or on the contrary to insert any electronic address. Abuse of uppercase or exclamation marks in the message will also be sanctioned.
Although all content is potentially usefull, some combinations trigger ISP anti-spam alerts. It is therefore good practice to know certain content rules to avoid having your email be sent to the garbage bin.