Deliverability rate is the percentage of emails that are directly received by the recipients right into their email box or Inbox.  Mails that land in spam box are not included in the calculation of deliverability rate.  

Deliverability rate is a crucial metric used by email marketers to determine the success of their email campaigns.  You need to follow a few steps to see to it that your emails are received correctly.  

Don't make your subject line appear spammy.  That's because subject line is the first thing looked by your email provider to decide whether to send it to the Inbox or to the Spam folder.  Avoid words that give spammy color to your email subject line.

Show a sense of value in your email prioritizing it with personalization so it gets dropped in the Inbox.  Don't make it look purely promotional.  Impress upon your email provider that your email is sent from your company's domain or a sercure IP address.  Ensure your DMARC protects you against phishing and it gives a good opinion about you as a sender to your email provider.

Deliverability is all about authentication provided by the email protocol to your email provider!   Remember subscriber behavior is also taken into account when your email provider thinks as to what is to be done to the email sent by you.  That means repeated unsubscribes can affect your deliverability much to your dissatisfaction.