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Once you have configured your email server, it is best to test it, login to your NMIS server and run the command /usr/local/nmis8/admin/testemail.pl, this will send an email to the Contact configured as Contact1. If you have problem you can run /usr/local/nmis8/admin/testemail.pl debug=true which will provide very verbose output for what the problem might be.
If you steel having problems with no test email in your inbox, please turn on you access for less secure apps, in the link https://support.google.com/accounts/answer/6010255
You will be able to see all the missing steps in you google accounts.