Turbo tax advised to mail to IRS my 2018 Federal estimate tax payments.
However, I was informed that https://www.irs.gov/payments/direct-pay allows me to make the 2018 Federal estimate tax payments on-line which seems easier to me.
Why not pay on-line then instead of mailing the actual check?
No reason not to. Although TurboTax prints mail-in vouchers for you, you can ignore them and pay online - just remember to pay by due dates.
I use Pay.gov to send hard earned money to our greedy Federal Gov.