It's an easy trap to fall into. Using your work email address for personal correspondence is wrong, though. Just as you wouldn't mix your business banking with your personal banking, you should take care to keep your personal and your business emails separate.
Corporate email policy
Does your company have an email policy? You probably signed off on it when you were hired - or it's a part of the company handbook. But did you read it? It probably uses language like this:
"It is strictly forbidden to use [Company’s] email system for anything other than legitimate business purposes. Therefore, the sending of personal emails, chain letters, junk mail, jokes and executables is prohibited. All messages distributed via the company’s email system are [Company]’s property."
If it does and you're getting personal emails at work, you're in violation of that policy. Even if the email is from your mother.
Leave work at work.
You shouldn't have to sift through your work emails to find the evite to your niece's graduation party. Keeping work and personal emails separate will help you keep work at work.
What happens if you change jobs?
If you change companies, voluntarily or otherwise, you'll lose access to that corporate email address. No one is going to forward corporate email to your personal account just so you don't fall out of touch with your high school buddies.