WLQ | caffe implementation of single level quantization | Machine Learning library

The problem you're hitting with MimeKit giving you an error about failing to parse the headers is due to the fact that your string is missing the message headers.

What you're effectively doing is asking a MIME parser to parse a message starting half way into the message. You're giving it an impossible task.

You need to combine the original message headers with the above string to produce the original (complete) message source before you can parse it.

Either that or you have to fake the original message headers so that things parse correctly.

Presumably you have the original message headers somewhere in your database?

Does the QuotedPrintableDecoder method need to come into play? I've reviewed http://www.mimekit.net/docs/html/Working-With-Messages.htm, but I'm hoping I don't have to manually traverse each part and there's still a way to grab just the message body.

There's generally no need to use any of the low-level decoders (or encoders) yourself.

There are multiple ways to get the message body:

1. Traversing the MIME tree manually (but in general I wouldn't recommend it), but to do this you really need to understand how MIME is structured and how common mail clients will structure their messages. It's not something I would generally recommend unless you are well-read on MIME. (Difficulty: Extreme)
2. Using a MimeIterator. For the most part, I wouldn't bother with this approach unless you want to manually traverse the MIME tree structure without using any sort of recursion. Where this class really comes in handy is if you are implementing something more akin to an IMAP server. Again, you need to understand how MIME works to really make use of this. See the documentation for a simple example on how to use this. (Difficulty: Extreme)
3. Using a MimeVisitor subclass to traverse the MIME tree structure. For a good example on how to do this, I would recommend taking a look at the HtmlPreviewVisitor class in the example in the documentation. This is probably the best way to do things if you want to "render" the message like a mail client might. (Difficulty: Moderate)
4. If all you want is the quick & dirty way of getting a message body and you don't care about trying to render the message the same way Outlook or GMail do, then you can use the MimeMessage.TextBody and/or MimeMessage.HtmlBody properties. (Difficulty: Easy Mode)

If I were you, I'd probably choose between the TextBody/HtmlBody properties and using something similar to the HtmlPreviewVisitor class in the example docs. They will be the simplest way to accomplish what you want to do.