Go to the gear up top right when in google email web page
Select "see all settings"  
Click on "Account and Import tab"
Click on Change Account Settings" -> other Google account settings
Click on "Security" on left  You can see if 2-step enabled.  Enable it if not. go thru steps. 
If it is.....  
Click on 2 step verification
Scroll down and click on app passwords 
Create a new password -give it a name and then create
generate code  -save this string someplace.

FOR pi3B and 3B+ imonitorg pis:
go to you rpi web page and click on mgmt.   
scroll down
Turn on gmail relay by entering YES [write over the "NO" -it has to be caps] and clicking submit button
Go back and enter your email in the gmail account "youraccount@gmail.com"  click submit
Go back and paste your 16byte key you obtained from gmail and click submit
Go back and enter "youraccount@hotmail.com" [e.g.]as the ultimate email [relayed by gmail] and click submit.  You can enter youraccount@gmail.com here as well.

You will receive an email at "youraccount@hotmail" [e.g.] each morning with stats and plots.

For pi4B iotsnoop
Edit the /etc/nullmailer/remotes file as follows:  [remove spaces in the letters gmail gives you]
smtp.gmail.com smtp --port=587 --starttls --auth-login --user-<your gmail adress user@gmail.com> --pass=<string from create above>   
Enter the ultimate email address you want to receive the file at as follows
echo "<ultimate email address, such as user@domain.com> > DEFgmailULTIMATE.txt