I believe that someone is monitoring where I send emails. Is that feasible? What can I do?
do you have some malwares on your pc?
Emails contain the IP address of the sender (although "the sender" may sometimes be a service such as GMail, so not always reliable), so a recipient may be able to tell where a message was sent from. At the other extreme, you may have spyware or a key-logger which monitors all activity on your computer. In between those, there are many other possibilities.
It would help us if you could provide more information. What makes you think that someone is monitoring your email. Is it a particular person you know? Are they in your household or somewhere else? Why would they be monitoring your email etc.