Gmail App search criteria - regex

Question

I have the following search criteria working very well in Gmail:
user#domain from:/mail delivery/ || /postmaster/ ||/Undeliverable/
I am trying to write Goole Apps code to return the same results. Here is the code:
var thread=GmailApp.search("user#domain from:/mail delivery/ || /postmaster/ ||/Undeliverable/ ");
I am getting different results. I am new to both Regex and Google Apps.

Answer 1

Try Amit Agarwal's tutorial on Gmail Search with Google Apps Script which includes Using Regular Expressions to Find Anything in your Gmail Mailbox:
function Search() {
var sheet = SpreadsheetApp.getActiveSheet();
var row = 2;
// Clear existing search results
sheet.getRange(2, 1, sheet.getMaxRows() - 1, 4).clearContent();
// Which Gmail Label should be searched?
var label = sheet.getRange("F3").getValue();
// Get the Regular Expression Search Pattern
var pattern = sheet.getRange("F4").getValue();
// Retrieve all threads of the specified label
var threads = GmailApp.search("in:" + label);
for (var i = 0; i < threads.length; i++) {
var messages = threads[i].getMessages();
for (var m = 0; m < messages.length; m++) {
var msg = messages[m].getBody();
// Does the message content match the search pattern?
if (msg.search(pattern) !== -1) {
// Format and print the date of the matching message
sheet.getRange(row,1).setValue(
Utilities.formatDate(messages[m].getDate(),"GMT","yyyy-MM-dd"));
// Print the sender's name and email address
sheet.getRange(row,2).setValue(messages[m].getFrom());
// Print the message subject
sheet.getRange(row,3).setValue(messages[m].getSubject());
// Print the unique URL of the Gmail message
var id = "https://mail.google.com/mail/u/0/#all/"
+ messages[m].getId();
sheet.getRange(row,4).setFormula(
'=hyperlink("' + id + '", "View")');
// Move to the next row
row++;
}
}
}
}