You can do everything as correct as possible, follow all of them recommended guidelines and do everything that the ISPs ask, but really the last wall is the mind of your recipient.
In the back of their minds your recipients know that your email is not spam because they went onto your website and put in their details so that they could receive it right? So you have that advantage. But there are just a few things that you need to be careful of to make sure that your non-spam emails do not seem like spam emails in the psychological spam filter.
1. Do not email too often. Depending on which sector you’re in of course. But if you’re an online store selling a product or products, I would say once a week is plenty.
2. Using the same subject line will trigger psychological spam filter into thinking that they have already seen the email. So switch that up.
3. The same thing with the template and layout, if your recipient thinks that they have already seen the email they will block it out, maybe have 4 different templates that you alternate.
4. The time that you choose to send your emails will also seriously affect whether the mind blocks out the email or not, sometimes there will be no right time, but help yourself out and send at a time that will be most convenient for your type of recipients.