It can be. Many companies have email usage policies which often include rules about sending and receiving work-related emails from personal computers. These rules are usually meant to prevent the accidental spreading of computer viruses that might have infiltrated a personal computer. Also, some companies are required to comply with Federal regulations on tracking and archiving company emails. 

If you really need to send work email from home, speak to someone in your IT department about getting secure access to your work email account from your home computer.