I assume your signature file contains images. These are normally included in th email. and they can be huge. Scalling does not change the size of the image file, just displays it smaller.

I found the problem!

Thanks Matt, that was a likely possibility though I had considered it and tried it without an image.

As I was working on my signature, I was saving older versions down below in my text file. They were blocked out as comments with , which was working as they didn't appear in the signature. But for some reason they caused the increase in e-mail file size.

I discovered it by accident. I'm stubborn and spent 45 minutes playing with the signature text, removing the image, parts of the text... trying to find the cause.

I decided I didn't need the old versions and deleted them, and the next test showed the problem resolved. By accident!

Thank you, Peter