_-_nox_-_ wrote:
I need the decrypted password to authenticate on the remote SMTP server
No, you don't.
Create single user to allow access to SMTP server via your application. Provide authentication to your application and use default user to operate on SMTP server. Log user activity.
That's all!
As Sergey mentioned, do not store encrypted/decrypted passwords in your application to log in into SMTP server.