BEE IN NOW
The developers were using Gmail account and password to send the emails dynamically. Less secure apps was used for it. That means you have to turn on that option in your google account.
Go to your google account. If you have multiple accounts logged in the system, Please choose the account where you want set the SMTP credentials.
Any SMTP setting will be a conduct of the credentials code. So now you will set the security for your SMTP app.
Go to the Security option from the left panel. Go to ‘2-step Verification‘ for the activation. (if it’s already ON then move to step-4)
After activating 2-step verification, you will find 'APP PASSWORDS' option in the security option. Enter in it.
In the APP PASSWORDS settings, You will generate app password by selecting app and category. You can select ‘Other’ in app and then add ‘SMTP’ in custom name.
After clicking Generate button, google will create one code. Here, the code is given in yellow background. Copy that code to use in your SMTP settings.