smtplib not working when python run under windows service via Local System account

[loial]

I have a python 2.7.10 script which is being run under a windows service on windows 2012 server .
The python script uses smtplib to send an email.

It works fine when the windows service is run as a local user, but not when the windows service is configured to run as Local System account. I get no exception from smtplib, but the email fails to arrive.

Any ideas?