I was assigned to the task to research how our clients news mail can avoid being marked as as spam. The emails requires use of HTML and showing images. Ive read alot of guidelines on the HTML and CSS when used in emails. But I haven't seen to many regarding the setup of the emails. I understand that pictures and links will increase the chance of being classified as spam. But what other factors are there? Does it matter from which SMTP server you are sending it? Does it matter if SMTP server relates to the sender email domain? I.e smtp:smtp.mydomain.com sender:email@example.com.
It's important to support a wide range of email clients. Should attached images be avoided completly?