Default "Contract Signed" email template with default attachments

I want the ability to compose a default message/email template specifically for when a contract is signed. Additionally, I would like the ability to attach default documents (like standard terms or brochures) to this automated response so I don't have to add them manually every time. This would help automate the post-signing workflow. Also, please look into the heavy black dashed lines that appear in MS Outlook for these emails.