How to permanently delete Mails within scripts via MailApp? - google-apps-script

Question

I have found the following script in this forum and works really smoothly (takes files, saves files in the right folder, etc.). Namely I receive a txt. file every morning with relative quantities which I would like to import and save to my Gdrive (to later use in other scripts). The file is named with todays date which I have used the Utilities.formatDate function to obtain.
Unfortunately every time I run the script I get all files from even from previous days which would spam my folder full in a couple of days. Therefore my question is whether one can delete the emails after the script that my google search query will not find the previous emails the following day?
Any help with this conundrum appreciated!!
P.S: Email comes from the same recipient, with an identical subject "Stock_Load", however the attachment is named "date"_Todays Date.
// GLOBALS
//Array of file extension which you would like to extract to Drive
var fileTypesToExtract = ['txt'];
//Name of the folder in google drive i which files will be put
var folderName = 'GmailToDrive';
//Name of the label which will be applied after processing the mail message
var labelName = 'GmailToDrive';
function GmailToDrive(){
//build query to search emails
var query = 'filename:stock_'+Utilities.formatDate(new Date(), "GMT", "yyyyMMdd").toString()+'.gpg.txt';
//filename:jpg OR filename:tif OR filename:gif OR fileName:png OR filename:bmp OR filename:svg'; //'after:'+formattedDate+
for(var i in fileTypesToExtract){
query += (query == '' ?('filename:'+fileTypesToExtract[i]) : (' OR filename:'+fileTypesToExtract[i]));
}
query = 'in:inbox has:nouserlabels is:unread' + query;
var threads = GmailApp.search(query);
var label = getGmailLabel_(labelName);
var Folder = DriveApp.getFolderById("XXX");
for(var i in threads){
var mesgs = threads[i].getMessages();
for(var j in mesgs){
//get attachments
var attachments = mesgs[j].getAttachments();
for(var k in attachments){
var attachment = attachments[k];
var isImageType = checkIfImage_(attachment);
if(!isImageType) continue;
var attachmentBlob = attachment.copyBlob();
var file = DriveApp.createFile(attachmentBlob);
Folder.addFile(file);
}
}
threads[i].addLabel(label);
}
};
//This function will get the parent folder in Google drive
function getFolder_(folderName){
var folder;
try {folder = DriveApp.getFolder(folderName)}
catch(e){ folder = DriveApp.createFolder(folderName);}
return folder;
}
//getDate n days back
// n must be integer
function getDateNDaysBack_(n){
n = parseInt(n);
var today = new Date();
var dateNDaysBack = new Date(today.valueOf() - n*24*60*60*1000);
return dateNDaysBack;
}
function getGmailLabel_(name){
var label = GmailApp.getUserLabelByName(name);
if(label == null){
label = GmailApp.createLabel(name);
}
return label;
}
//this function will check for filextension type.
// and return boolean
function checkIfImage_(attachment){
var fileName = attachment.getName();
var temp = fileName.split('.');
var fileExtension = temp[temp.length-1].toLowerCase();
if(fileTypesToExtract.indexOf(fileExtension) != -1) return true;
else return false;
}