Navigation bars in email
My personal recommendation is don’t do it. You’re already dealing with limited space and the user’s limited attention span. Lets not complicate things. I don’t have any stats to back up this opinion, so feel free to present some metrics to prove to me that it is worth it.
Building responsive emails
A list of things to remember when building responsive emails:

• Use !important in your media queries to over power inline CSS
• Apple recommends minimum button height be 44px on mobile devices
• Create your images @2x for retina displays, and remember to set the height and width otherwise they will break Outlook
• Remember to compress those images to reduce the file size
• Keep subject lines fewer than 50 characters
• Preheader text is even more important on mobile
• Minimum font size on mobile should be 13px, recommended is 16px for text and 22px for headings
• Don’t use navigation bars in emails
• Your best bet is to stick with a single column layout, much simpler than supporting multiple columns
• Sure you can use grids it just gets a bit trickier and requires some conditional hacks for Outlook
• Don’t forget your landing pages should be responsive too
• iOS styles links, dates, addresses and phone numbers as underlined blue text, to get around this have a media query class to override
• Use px over ems
• Use Margin not margin (capital “M”) so margins work in Outlook.com