Responsive email design is basically the same as responsive web design, but it applies to emails only. What this means is that sent emails will be loaded with flat images, tables and etc. and also be able to adapt to different devices such as smartphones and tablets.
The precise year or date of responsive email design is unknown. This development rule has been among us since 2000, but email response became used and popular in the last couple of years.
Regardless of what you are or why you use a website or emails, responsive email design must be used. It is extremely important due to the fact it allows for the users to read and reply to email messages from different devices. Without this design, most emails will be discarded without being read first.
Marketers should use responsive email design simply because this increases the chance of a user reading and interacting with the email. It is essential for email marketing and it must be used regardless of the purpose of the campaign.