The quarterly payment vouchers printed by Turbotax do not fit the IRS-provided window envelopes.

Do you mean the 1040ES vouchers so that you can send in quarterly estimated payments to avoid an underpayment penalty at tax time next year?  Not sure why you think those are supposed to fit an "IRS provided window envelope."   If you need appropriate envelopes--you can purchase envelopes from many retail stores and write the address on the envelope yourself.

Yes, the Quarterly payment vouchers. So, explain to me why I should BUY envelopes when the IRS provides them--along with the vouchers--at no cost? The problem exists with TurboTax. The software has not been updated to fit the standard window size of IRS envelopes. 

To call TurboTax customer support

https://ttlc.intuit.com/questions/1899263-what-is-the-turbotax-phone-number

Customer support is available from 5 a.m. to 9 p.m. Pacific time daily

An alternative---use the IRS web site to make the payments:

https://www.irs.gov/payments

Thanks, but it's so much easier to use the IRS-provided materials and merely fill in the amount. Meanwhile, the TurboTax programmers need to fix the problem.

I just got my IRS package today.   The 1040ES slips are preprinted with my name etc.  All I have to do is write in the amount.  Couldn't be simpler.  

Yes, the ones thar TurboTax prints are worthless.