To be able to send email marketing to inbox. You need to buy SMTP of famous services such as Amazon's email service, Sendgird ... etc. 

To use our Email Marketing service effectively! There are following steps you need to do:

Step 1: Buy Unlimited SMTP Server here: https://smtpzo.com/67-smtp

Step 2: Contact Admin to ask us to filter your email list. All emails that only deliver Spam / Junk include:

@gmail.com
@yahoo.com
@outlook.com
@live.com
@hotmail.com
@aol.com
Office365 Domain Mail
Emails aren't value
Email traps from anti-mail organizations.
...
etc

All of the above types of emails should be removed from your email list.

Step 3: Send mass emails.