I just received a suspicious mailing claiming to be the IRS. They are asking me to mail the first two pages of my tax return to them within 12 days. Is this legitimate?

A letter or e-mail?   The IRS only send letters with a government address.   They do not e-mail - they do not even know your email address.

Sounds like a scam.

It was mailed in an envelope but the address doesn't seem to be a U.S. Govt address.

Does it have a notice or letter number on it like a CP2000 or other number?

no.  It is mailed from 5045 E. Butler Avenue, Fresno,CA

I would like to get Turbo Tax to respond to this question.  How do I do that?

I received one for 2016 tax return. The address I recieved is different from when I Google the address.

If in doubt call the IRS to confirm.  There are scammers that are sending mail.

That would appear to be a real IRS address.

https://www.irs.gov/irm/part1/irm_01-022-003.html

"Street Address - The street address for each Campus/Submission Processing Center/Accounts Management Center is shown below. All general administrative mail and/or SPC deliveries (e.g., UPS and FedEx) from IRS and other sources should utilize the following street addresses:"

"Internal Revenue Service
5045 E Butler Ave
Fresno CA 93727-5136 "

You can contact TurboTax Customer support this way:
https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number?jump_to=answer_3300041

https://ttlc.intuit.com/replies/3300041

5045 is an IRS MAILING ADDRESS, had been since the 70's. Sounds like you got a notice for missing info from the ERS Dept.

Do you have a fax number for it

If it is acceptable to fax the two sheets, then the fax number would be on the letter. Otherwise, you can't fax it.

Are you, too, saying that there is no Notice number on this letter?