Add a Background Image to Your HubSpot Email Template (Custom Module)
This one seems to come up a lot (I've had plenty of client requests and see a few posts on the community) and has caused me endless hours of banging my head against the wall so I thought I'd share how I've been doing it.
When testing across clients it seems to work on most of them (yep, even Outlook). You'll probably still want to do some tweaking to padding, widths (my logo's a bit large on mobile on the above, for example, and a 600px image should help with displaying more of the background on Gmail), etc. but it should mostly work.