Is it an email that you are sending to someone and it is being sent to everyone in your address book, or is it a spam email that you have not personally sent to anyone?
Which email are you using? and what is your operating system?
Do you have Malwarebytes installed? If not:
Then, please download
MalwareBytes' AntiMalware
* Double-click
mbam-setup.exe and follow the prompts to install the program.
* At the end, be sure a checkmark is placed next to the following:
o Update Malwarebytes' Anti-Malware
o Launch Malwarebytes' Anti-Malware
* Then click
Finish
If an update is found, it will download and install the latest version.
* Once the program has loaded, select > Perform Quick Scan, then click > Scan.
* When the scan is complete, click > OK, then > Show Results to view the results.
* Be sure that everything is checked, and click > Remove Selected.
* When completed, a log will open in Notepad. Save this log to My Documents in case it is needed for reference.
Reboot as required.
Also update yuor antivirus softawre and reboot your computer into Safe Mode and run a full antivirus scan. Delete everything it finds.
If the scans prove negative then it may be that the malware is on someone elses computer and is using the addresses that it has found in the 'To' or 'CC' address section on emails that you have forwarded to someone.