The most common reason for your emails getting marked spam is this -
When people to whom you are sending these emails, mark your email as spam
You are a tea seller who is doing cold email outreach, you reach out to everyone in your city where a group of passionate tea haters also live. Once this email reaches out to them, they start marking your email as spam. This is what happens when a salesperson adopts the spray and pray method when they use email outreach.
Always send your emails to your target audience only, to avoid this scenario.... (More)