If your contract specified that termination could only be done by registered mail, then Fed-Ex, while similarly provable, would not suffice.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Technically it doesn't comply if it doesn't do exactly what the contract says. Whether or not the termination is still valid, however, is a larger question involving the language of the contract and your state's substantive law.
Disclaimer: This answer is provided as a public service and as a general response to a general question, it is not meant, and should not be relied upon as specific legal advice, nor does it create an attorney-client relationship.
