The worst thing you could possibly do if you are in business on the web is to change your email address. I've had the same email address since the early twentieth century, and see no reason to change it. But this doesn't stop many people from changing their email address and sending out a message to their friends to "send to that new address".
If you always go back to a previous email from someone to send an email, it isn't much of a problem. I don't, because I find it a time-consuming and laborious process to plow through all of my old emails to do a reply, so I use the autofill feature in Mac OS mail. I just start typing the name and it remembers and fills in the rest. This works great, unless there are old addresses. Then you have to eliminate them. This is how you do it: