To figure out your email cost:

  1. Log into your SMTP provider, navigate to the Plan or Billing section and look for a description of how many emails are included in your plan. 
  2. Once know the amount of emails in your plan, divide that by the cost of your plan and the result will be your email cost. 

For example, the $35/month Mailgun plan includes 50,000 emails so 35/50000= email cost of $0.0007