Email is the cheapest direct marketing channel. It is powerful because you can directly contact your clients or prospects, and the best part is that sending email is way cheaper than other direct communication channel. A properly managed email marketing campaign helps maintain relationships with existing customers and inculcate brand consciousness into prospects, and hopefully convert them into paying customers.
A key factor to a successful email marketing campaign is the cleaning of the email address list used.
Many email service providers (like Gmail, Hotmail and many others) evaluate the quality of the email you send every day using specific metrics.
These metrics can trigger the service provider blacklist flag for you, and when it happens emails that normally would be delivered to your recipients are blocked.
As you can imagine this is very bad for your email marketing campaign!
As people are constantly moving, emails sometimes get lost or forgotten.
This happens, for example, when your contact gets a new job, change the Internet provider or simply decide to create a new email.
Sometimes users voluntary subscribe to your service with wrong or disposable addresses (in the case you are wondering, there are services where you can get an email address for one day).
All these events generate invalid email addresses that stays in your email list and increase your "bad email rate".
For the list of emails you already have, you can simply use Emailrazor file validation service and validate the whole list, discarding all the unreacheable or risky emails.
Once you cleaned up your current list, you should avoid to add bad emails to it again. To do it, you can use Emailrazor api and check whether an email is good or not in the very moment the user subscribes your list.
Finally, don't forget to always offer to your users a simple way to unsubscribe from your list, because if they can't easily unsubscribe they will click the "report as spam" button!