Gmail lets you change the subject of a reply or forwarded email, but the option is a little hidden. This is particularly useful whenever you must reply with “UNSUBSCRIBE” in the subject line to be taken off a mailing list.
To do this in the web version of Gmail, click the “Reply,” “Reply All,” or “Forward” option to start composing your reply or forwarded email.
Click the button to the left of the “To” field and then click “Edit Subject.”
Gmail will show you an email compose pane with an editable subject field. Change it to whatever you want—you could add the word “UNSUBSCRIBE,” remove the “Fwd:” from a forwarded email, or write a new subject line.
That’s all you have to do. Click “Send” to send the email when you’re done composing it.
On the Gmail app for your phone, this is even easier. While composing a reply or forwarded email, the Subject line will appear and be editable above the body of the email. Just scroll up and change the subject to whatever you like.