Hi Hashir,
Thanks for providing further details.
Could you try executing the simple script below for sending email? You can specify the email address that you've set on the other script, please observe if you experience the same issue. If the issue will also occur on this simple script, then I would suggest reaching out to the Google App Scripts team via this
support link as the issue is more on MailApp and this is out of our expertise already.
MailApp.sendEmail('
your_...@domain.com', 'test', 'test');
Regards,
Ejay