There is no silver bullet for this, but there are ways to mitigate the effect. However always remember that email spam rates are a way of saying that the email

There is no silver bullet for this, but there are ways to mitigate the effect. However always remember that email spam rates are a way of saying that the email is not interesting enough If a user marks you as spam, unsubscribe them from the email. Make sure your content is interesting enough for readers to actually read it and possibly respond. If it is not, you may want to spend some time rewriting it and adjusting the copywriting You may want to adjust the times you send out the information. If you're sending email in response to signups you may want to send it around half an hour after signup. Try to time it for when users will actually read it (so usually non-Monday or Friday weekdays) Always make sure to have a one-click unsubscribe button in a fairly obvious location. If a user wants to unsubscribe they are likely to hit spam if they can't find the unsubscribe link. You can give users whitelist instructions, although frankly I don't know how effective this is.