Include the following information with your issue:

1) Nodemailer version you are having problems with (eg. v1.3.0)
2) Node.js version you are using (run node -v to see it, eg v5.5.0) 
3) Your operating system (eg. Windows 10, Ubuntu 14.04 etc.) 
4) If possible, include a minimal test case that can be used to verify your issue (link to a gist would be great!)