Add an API for validating email addressess
Add an API call for validating email addresses (i.e. checking whether the domain is valid, the username exists, the mailbox is not full, etc..) similar to kickbox.io and make it affordable/free to use :)
David Garcia commented
I don't know your development code, but for example PHP has this vendor that is used to validate the email address: egulias/email-validator (you can find more details here: http://symfony.com/doc/current/reference/constraints/Email.html#strict)
I am sure other languages have other packages to validate email addresses. Maybe, depending on your project requirements, you can validate your own details on your development, instead of expect a validation from a 3rd party environment, given is your code the one that is requesting EMail addresses and it's you who is sending all messages.
The idea is: what happen if some day you want to change this service and use another provider? Maybe the other provider is not validating the EMail address, so you will need to create the same request again, will wait for an approval and the required development.
From a developer perspective, this is a delay that cannot be accepted.