Do you have proof of having mailed it before the three days was up? It is going to come down to your word against theirs, and if the post-mark is more than three days after the contract date, you may have a serious problem defending their claim to being entitled to some damages. 1/2 of the total cost of the job might be excessive, but the problem is that they will almost certainly file a mechanic's lien, and then pursue you in court. They may also simply elect to sue you. I would suggest that you consult with a local attorney who handles construction matters to review the demand letter from the window company, to review the contract for any other possible "outs," and determine your best course of action.

*Due to the limitations of the LawGuru Forums, The Gibbs Law Firm, APC's (the "Firm") participation in responding to questions posted herein does not constitute legal advice, nor legal representation of the person or entity posting a question. No Attorney/Client relationship is or shall be construed to be created hereby. The information provided is general and requires that the poster obtain specific legal advice from an attorney. The poster shall not rely upon the information provided herein as legal advice nor as the basis for making any decisions of legal consequence. As required by 11 U.S.C. §528, we must now disclose that, "We are a debt relief agency. We help people file for bankruptcy relief under the Bankruptcy Code. Assistance we provide with respect to Debt Relief may involve bankruptcy relief under the Bankruptcy Code."

I agree with Mr. Gibbs. I would add that attorneys often have to deal with the late-postmark issue because we so often have to serve papers by a certain deadline. In my small town, the last mail leaves the postoffice before 3 p.m. and Saturday dispatches are not guaranteed, so it's entirely possible for me to mail a document at 3 p.m. Friday and it to be postmarked at the regional mail processing center on Monday a.m. For service of papers, that complies with a Friday mail service. If handling by the U.S.P.S. may be a factor, check the collection times at the box or postoffice you used. Also ask the contractor for a copy of the postmarked envelope.