I have a multi column email, which works on every email client but something very funny happens on GMAIL and i am scratching my head as everything appears to be correct. What is funnier is that GMAIL on desktop is fine and it is only GMAIL app on android and iPhone which is behaving strange.
Have you checked LITMUS which teaches you all the basics of email's. GMAIL is notorious is stripping the head element all together. https://litmus.com/help/email-clients/gmail-no-head/