If you were emailing Pet Care Companies in order to have them print their advertising materials through you, what would you make the Subject of the email? Pet Care Business Flyers Get your advertising flyers cheap ...etc any ideas??
If I was a Pet company and got this email when I was not already on your mailing list it would be called spam. ;p You need to get more personal with the email and contact them direct via email and prob phone.
The name of the company you are emailing. A pain, but it works. ...and yes, if it is unsolicited, it is spam. No matter how good your service may be. Most email providers will block it anyway.