If you are using email marketing to promote your business, you need to clean your list every six months to a year. You do not have to just remove subscribers from your list, you can send them a series of about three emails to try to win them back.
You can use a subject line of say “Are we breaking up?” for the first email to try to get them to open the email and engage with it. Ask your subscribers if they want to continue to receive your emails. You can then send them two more emails in an attempt to salvage them.
The most important reason that you want to have a clean list, is that it will help you with your email deliverability. More of your emails will get into the inbox. Email providers like Gmail and Yahoo are looking at what your subscribers are doing with your emails and if they are engaging with them. If they are engaging in a positive manner, they will send more of your emails to the inbox. If they engage in a negative manner, it will lessen your chance.
Forms of engagement would be opening, clicking, forwarding, starring, marking as important and also removing your email from the spam folder, marking as “not spam”. Negative engagement would be ignoring, unsubscribing, deleting marking as spam and bouncing. This type of engagement hurt your inbox placement.
Identify people who have not opened your email in a while (six months to a year) and run a re-engagement campaign. Remove the subscribers that do not show they still want your emails. You can always add them back later when they show interest.
If you would like to talk about best practices for list hygiene, let me know.