If the supporting documents submitted by you along with your immigration petition are insufficient and if the USCIS officers require additional supporting documents, they will send you a Request for Evidence(RFE). A Request for Evidence will be made if your application lacks the required initial evidence and if a USCIS officer requires more documents to determine your eligibility for a particular immigration benefit. USCIS will send you a Request for Evidence while processing your application. This notice will contain the address where you must mail your evidence and the date before which you must send the required documentation. You may contact the National Customer Service Center by dialing 1-800-375-5283, if you have questions or doubts.
Your case will be denied if you fail to send the required documents before the deadline and if you fail to respond to the RFE. After you respond to the RFE, USCIS will review the documents that you send and will decide on your case. You can avoid an RFE, if your immigration petition is well prepared. However, you need not worry if you receive an RFE, as RFEs are common. But you need to carefully deal with an RFE and respond to it before the deadline and you must read the RFE carefully. You need to remember that you may not be given additional time to respond to an RFE. If you miss the deadline and if your immigration petition is denied, you may appeal or you will have to start the application process again.
Moreover, a Request for Evidence and a Notice of Intent to Deny, are not the same. And if you receive a request for evidence, it does not mean that the USCIS will deny your petition. Nevertheless, while responding to an RFE, make sure that you send all the documents that you feel are relevant and that will help the USCIS to decide on your case. If your documents are not in English, send certified translated copies.