I've had to file two late elections this year. First client - prior CPA never mailed it in.  Second client said they mailed it but no approval letter (after a year) and reject on extension due to entity mismatch.  How to is very clear in the 2553 instructions.  I called the IRS and they said taxpayer must mail in a paper return along with the 2553.  Who am I to second guess the IRS????