Strange SPAM

I use Thunderbird for email. My filters have been working fine and all has been well until about 6 months ago. On an email account that is reserved for very limited communication with a select few, I inadvertently use it to send a message to a less computer literate friend. She saved it and despite my request to delete it, she retains it (though she thinks I think it's gone). I suspect someone got hold of here address list and my special email address is one it. No matter what I do, I cannot filter out emails that contain a strange character. Here's an example:

In desperation, I've begun looking for another email program. I stumbled upon "Mailwasher". It claims to be compatible with Thunderbird and appears to have the capability of blocking mail such as the above... though I thought Thunderbird was capable as well.

Can anyone tell me anything about this character embedded type email, how correct I may be about getting on there list, and if I'm moving in the right direction with "Mailwasher"?