The unread mail count is wrong / never updates, and clicking on the extension icon no longer brings up a tab with Gmail. Turning the extension off and back on again fixes it for awhile, but then it inevitably stops after some indeterminate period of time.
Within Send Mail As, click Add Another Email Address You Own. Enter the email address you'd like to send mail as. Step 3. Enter the secondary email address. You may also edit the displayed name and specify a different reply-to address. Gmail prompts you to verify the secondary email address. Send the verification email.