I am writing a small script in a Google Sheet to automate sending tasks to a large number of users (~low 100s). Each message is personalized with the details of the request for each recipient, and I would like to start with "Hi {firstName}" rather than be impersonal. Currently I do the lookup by hand, but now that the numbers are going into the hundreds it is becoming tedious, time-consuming and error-prone.
Our email system is hosted on GMail with our custom domain. I am not an admin and won't be given (or ask for) permissions to be one just for this.
Is there a way available to a regular user to script the lookup of the Global Directory so that I can get a full name given an email address?