Send mail from POP account but goes from Zoho account

Send mail from POP account but goes from Zoho account

We have over 30 enterprise users. Most all of us are experiencing a very strange and serious problem. We have our default email set as one of the POP accounts. Sometimes when we send an email it never arrives. Also we send an email from our default POP account but it goes to the recipient from our Zoho account and we have no idea how this is happening. Please let us know if this is a bug or if there is some setting we need to change. This starting happening a few months ago and it is embarrassing and confusing to both our clients and our employees.