The source code is there too, but I wouldn't look too closely. "Cobbled together", like I said. Though I've been using it all the time, in conjunction with ag-mode - https://github.com/Wilfred/ag.el - and haven't noticed any obvious problems.
I've used this in the past but came away disappointed as it regularly breaks over attachment sizes. I was using it to store my website backups in dropbox.
Instead of this, now I setup a simple python dropbox script on my webserver which allows me to do few good things:
1. No connecting to third party apps.
2. No need to go through email servers, I can directly store the backups to dropbox
3. I still added an email addon layer on it for other usage where I send the files to my own mail server and the script then puts them into dropbox.
True..I try to avoid volatiles as much as I can. And as someone else pointed out on the blog in the commens, many implementations even get the volatiles wrong giving rise to a lot of bugs, so even if you were utmost careful about it, it can still cause issues.
Yes, using portable data types is much easier. But I thought about this when we had to make our code work with some legacy code (which we couldn't change) and the outputs were in non-portable data types.