Yes. You can check the status and it will state whether the response to an RFE is being considered.
I always send documents to a government agency by certified mail with a signature required - at a a minimum by a method that can be traced. This way we are always able to confirm receipt. You should also make copies of everything you send to them.
In general, the USCIS website will indicate receipt of your response. However, that site is not 100% accurate. The best practice is to submit any documentation using either a courier or registered mail. In doing so you will have proof of delivery. If you do not have proof of delivery and you are still within the period of time that USCIS gave you to respond you may consider resubmitting using either a courier or registered mail.
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The best way is by sending in through FedEx or some other carrier that allows you to track it.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.