How does Gmail's inbox show a track order button in the end of a subject line for e-commerce mails -

a track order button appended end of subject line in gmail's inbox. how it?

that because e-commerce company receive emails might have whitelisted action button displayed.

those buttons called action buttons , smartmail feature google access data without opening email.

in order companies email whitelisted can register email following guidelines mentioned google in page.

hope helps!