In order to retrieve the SMTP password of your Pepipost account, please follow below steps,
1. Login to your Pepipost account.
2. Go to settings =>integrations as shown in below image
3. Once you reach here you can see your encrypted SMTP password under section "SMTP Relay"
4. Please click on "Show" button and enter your login password again to verify yourself and see your SMTP password.
You can copy the password from this section and have it configured within your application.