|What email package/app are you using to send emails?|
Is the response you posted applicable to any email, sent to whomever/wherever?
Any changes to the installation prior to the problem arriving.; any other "effects/events" prior to the current problem?
Do you have restore point from earlier?
Have you run any malware/pest removal utilities since the problem arrived... It "may" be that you have a pest or three involved, hence the suggestion re' malware/pestware utilities...
There are several you might consider anon..