When someone clicks the "View online" link in your email message (generally placed at the top), you will notice the email has a "title" which displays in the web browser on the tab - as shown below.
For new emails, this title is generally derived from the subject line - but if you're copying an old email to build a new one, the title from the old email will be used. However, you can change the title at any time.
- Select Messages from the sidebar.
- Open your desired email for editing.
- Select the Design tab to the right and expand the Email Settings panel.
- Adjust your email title in the View Online Title field.
- Click .