I live in Colorado, should I mail the forms to Austin, TX or to San Francisco, CA?
Mail Form 8453 and Form 8949 to
Internal Revenue Service
Attn: Shipping and Receiving 0254
Receipt and Control Branch
Austin, TX 73344-0254
Where to Mail 9465 (scroll down)
The answer depends on a number of factors. See <a rel="nofollow" target="_blank" href="https://www.irs.gov/instructions/i9465/ch01.html">https://www.irs.gov/instructions/i9465/ch01.html</a>