Hi Allan,
Circling back to the issue of Assign Form node in Nodered.
There are items that slightly go above this 512KB limit, is there a way to overcome it?
Thank you 
No. If you are that high, most likely you are trying to store files as part of the data? In that case, you should be using work items and store them as real files in GridFS (you can map those to file components in the form as well if you need to allow the user to upload or download files).
I actually send email html, to display an email inside the form. The user has the email to be processed on the left have side, and some control on the right half. The issue occurred with long email threads
Yeah, I can see how this kind of “fits” into both camps…
I would recommend you store the original as a file (.eml) and then extract the important part from bigger emails when needed, and store it in the payload for easy access.
We could remove the limit, but that will only help a little since MongoDB does not allow storing more than 2MB as JSON documents (and it performs BAD when they are bigger than 700KB). This is why it’s important we store big/binary data as files using GridFS