Set Value on a DIFFERENT Sheet in Google Apps Script
===

I want to do a variation on the ["Sending emails from a Spreadsheet" tutorial on the Google Developers page][1].

I want to do exactly what they walk me through EXCEPT that when it comes to marking the cell in each row every time the e-mail is sent, I want to mark that on a SEPARATE sheet.

So, on the sheet "NeedReminders", my script finds the e-mail addresses of members to whom the e-mail should be sent in column A (which then becomes variable "emailAddress"). It sends the e-mail to that address.

THEN--and here's where I need help--I want the script to go to the "Master" sheet, find the row where emailAddress is in column X, and--in that same row--set the value of column BT.

Shouldn't be difficult. I just don't necessarily know how to do the "find the row where columm X equals emailAddress and set value of BT to today's date" part.

Who can help? Thanks in advance!

Here's my code so far (I'm always embarrassed to show my code because I'm sure it's terrible juvenile, so be gentle, please!):

    function sendDuesReminder() {
      var sheet = SpreadsheetApp.openById('___').getSheetByName('NeedReminders');
      var startRow = 4; // There are a bunch of headers and other nonsense.
      var valueSheet = SpreadsheetApp.openById('___').getSheetByName('Master');
      
      // Determine how many rows to process
      var rowRange = sheet.getRange(3,4); // On my sheet, cell D3 counts how many members are on the list of people who need a reminder e-mail.
      var rowData = rowRange.getValue();
      // End Determine how many rows to process
      
      // Send e-mail
      var dataRange = sheet.getRange(startRow, 1, rowData, 2);
      var data = dataRange.getValues();
      for (i in data) {
        var row = data[i];
        // var emailAddress = row[0]; //Column A: E-mail Address
        var name = row[1]; //Column B: First Name
        var subject = "Reminder About Dues for Newcomers & Neighbors";
        MailApp.sendEmail("matt@twodoebs.com", subject, "Hi, " + name + ". It's been some time since we received your online registration for Newcomers & Neighbors. But we don't seem to have received your dues payment, yet. So we wanted to drop you a quick line and remind you about it." + "\n\n" + "If you think we should have received your payment by now or there's some kind of a mistake, please let us know by responding to this message." + "\n\n" + "Otherwise, please send a check for __ made payable to ___ to:" + "\n\n" + "___" + "\n" + "___" + "\n" + "___" + "\n" + "___" + "\n\n" + "Thanks! Please don't hesitate to reach out if you have any questions." + "\n" + "___" + "\n" + "___" + "\n\n" + "Best wishes," + "\n\n" + "Kati" + "\n" + "Membership Director",
                         {name:"___"});
      
      // End Send E-Mail
      
      // Set that an a-(Experimental)
      var valueRange = valueSheet.getRange // Here's where I kind of break down . . . I need *something* here that searches the sheet for emailAddress
      setValue(today()) //I'm also not sure that this is the right way to set the value as today's date
      SpreadsheetApp.flush();
        // End Set value
      }
      Browser.msgBox("OK. Reminder messages have been sent. doebtown rocks the house!")
    }


  [1]: https://developers.google.com/apps-script/articles/sending_emails