Step 3.c Receive a response
When Adele receives your email, she will use her private key to decrypt it, then fetch your public key from a keyserver and use it to encrypt a response to you.
Since you encrypted this email with Adele's public key, Adele's private key is required to decrypt it. Adele is the only one with her private key, so no one except her — not even you — can decrypt it.
It may take two or three minutes for Adele to respond. In the meantime, you might want to skip ahead and check out the Use it Well section of this guide.
When you receive Adele's email and open it, Enigmail will automatically detect that it is encrypted with your public key, and then it will use your private key to decrypt it.
Notice the bar that Enigmail shows you above the message, with information about the status of Adele's key.