Email Signature low resolution, looks good when saved...

What format are you exporting to? Looks like Outlook is doing some pretty awful compression. I can't advise on what Outlook settings might help.

It would probably better to upload a PNG of the design somewhere, and code an HTML signature that references it. This will also avoid it being an attachement, which isn't good practice. You should be able to find quite a few turorials for doing this online.

The only way you might get an acceptable result is to (if you're running Windows), export your composition as .emf, and import it to Outlook's signature editor using the Insert Picture feature.

Nevertheless, I interpret Monika's advice as "forget having a banner ad as your email signature," and I'm inclined to agree. There is too much deatil in your design to effectively serve that purpose and render reliably in the potential variety of email clients. I'm also inclined to mention my personal take on it, which is: if I was someone who regularly received emails with a graphic like this at the bottom of each one, it would annoy me to the point that I would block the sender or turn off image download. Burdening your email recipients with this kind of spam-bloat is discourteous.

Just forget that. There's too much information in your tiny image. Once you convert it to pixels then you can zoom into it endlessly anymoe.