Thunderbird question

Whenever I sent an email using Thunderbird, the person that receives it read it like this:

The problem is this >. What do I have to do in order to fix this?

Process of elimination:

Is that how you see it when they reply, quoting you? If so, that’s just standard e-mail notation for “This is quoted material.”

An interesting question. But this is the SMDB so I sent myself an email to test if the
> is present:

You Sir are a light in the dark.