Outlook 2007 Fuzzy Email Signature

Have created a signature in Indesign, exported as EPS, opened in Photoshop and saved as a PNG. Have inserted the PNG file in the email signature. If the email is printed before it’s sent it crisp but after it’s sent to the recipient and printed it’s fuzzy. How do I fix? Have tried other formats including JPEG & gif and all are fuzzy, just some worse than others.