Unreadable mail

I get from some of my clients mails like at the picture. A mail is splitted int two parts with attachments and text lines.

These clients have reliable addresses. Sometimes I get correct mails from them. It’s look like a spam filters do it, but I’m not sure.
I made a filter, which puts mail from these specific address to a named folder. However, these mails I find in dumpster folder.

this is the folder I’ve mentioned: