Article in English: As soon as you’ve proofread your draft, and prior to sending it off, take a photo (transfer to pdf), save a draft online, or make a traditional copy of your letter. You may also want to write down the mail off date if it doesn’t match the one at the top of the letter. File this copy somewhere safe for your personal record. Take your letter to the local post office, give it to your mail carrier, or drop it in a post box. If you want more assurance that your letter was received you can always request extra tracking services for an additional fee. If you are going to mail off a hard copy of your letter, make sure to print it out using a high quality printer with a good ink cartridge. A handwritten extension request is generally not acceptable. This is the probably the best way to send your request as it requires little time and is very reliable. Verify your recipient’s email address before sending and include your identification number, if relevant, in the subject line.  Your recipient may be able to see the exact time that you sent the email. Be aware of this if you like to send off emails very late at night. Keep your email formal and that includes the address that you use as well. Send this email from a professional-sounding account. For example, sending a work email from “John.k.Smith@yahoo.com” is appropriate. If you send your letter via fax, make sure to hold on to the confirmation page showing that your transmission was successfully sent and received. If your need for an extension is urgent or very last minute, you may be better served by talking to them in person or by calling. If this is the situation, continue to act formally and state your case in an organized way.

Summary in Vietnamese:
Sao lại một bản hoặc lưu lại bức thư. Cho vào thùng thư thông thường. Gửi thư xin gia hạn qua email. Gọi điện thoại thay vì viết thư.