With email marketing services such as Mailchimp, you're guilty until proven innocent. You need to clean your email list before you can send your email newsletter to make sure you're not sending SPAM.
Because email services rely on their servers staying squeaky clean your old email list poses a threat to their ratings. Every mail server sending bulk emails runs the risk of being blacklisted if they send too many bad emails. Therefore they will run a series of checks to ensure your email database, and the emails you send, make the grade.
What is a bad email?
If your email list has known "trojan horse" email addresses (addresses that spammers use to find valid email addresses). If you have too many bounces you will get flagged by mail servers who will assume you're trying to spam everyone. And, if your email address list has generic email addresses, for example email@example.com, then your list is not considered a quality list.
"If your list is anything below A grade you could be blacklisted, or your account could be suspended."
How to clean my email list?
There are several online services, like Data Validation - which plays nicely with Mailchimp, that will run your email list, one by one, through a series of tests to see if the email addresses are valid. At the end you will receive a list of the good, the bad and the ugly. By filtering the list in a spreadsheet you can then upload a clean set of emails and start marketing to your list.
Tip: To save time and money, merge your list in a spreadsheet and remove duplicates before you upload it to a cleaning service.
But what about the others? Surely I don't have to delete half of my database.
Is it really worth the risk? Your email list, in most businesses, is your income. Without a list of quality names and email addresses it's much harder for you to run a campaign to land new business when things are quiet. So, you're still not convinced? What happens if your account is shut down, or your server is blacklisted? Then all your emails are useless and you'll have lost hours trying to reinstate your account before you have to go back and clean your list anyway.
So, if in doubt, delete them. With a good lead magnet and a compelling call to action you can build up your database with quality leads.
Tip: If you're starting your email campaigns for the first time you want to introduce your contacts to the concept before you start emailing them. Often you'll be starting with a cold list (if you haven't been in touch with them recently).
If you don't take responsibility for the quality of your email list then someone else will and you'll have your account shut down or you'll be blacklisted.