I've been told I have to mail in some forms even though I filed electronically but never been told exactly what do I have to send and to whom. Any ideas?

[Opus 17]

Which documents?  There are a number of situations where you might need to attach extra information.  There are 11 specific forms that you can mail to the IRS after e-filing.  If you are not in one of those situations, then the only way to attach the document is to print your return and file by mail.

If you are in one of those 11 situations, print your return.  There will be a cover page with instructions, and it should also automatically print out a copy of form 8453, which is a cover page.  Put the needed form and the cover page in an envelope and mail them to the address indicated in the instructions for form 8453. 

[DawnC]

If you received a request to submit Form 8453 (US Individual Income Tax Transmittal for an IRS e-file return), you need to mail some forms to the IRS that can't be e-filed.  TurboTax creates Form 8453 for you, and it serves as a cover page for your additional documentation.

Mail Form 8453 to the IRS within three business days after you’ve received your acknowledgement that the IRS has accepted your return to this address:

Internal Revenue Service
Attn: Shipping and Receiving, 0254
Receipt and Control Branch
Austin, TX 73344-0254

Click here to see a list of forms that can and can't be sent with Form 8453.