When do my emails get marked as spam?

At Mailercloud, we want you to follow good email marketing practices to avoid spam. For instance, if you have been sending too many emails with an unverified email ID, sending spammy subject lines, sending emails without taking the recipient's permission, avoiding domain authentication, using poorly designed email templates with little emphasis on texts, using emails for unlawful activities and other such scenarios, you might be marked as spam. This is also essential because your emails will affect your existing users and risk our platform's reputation.