Does Mark to market election under sec 475 for first time for 2019 prevent me from e-filing for 2018?

[twistedether]

I understand that TurboTax does not support making the MTM election so you will have to paper file your 2018 return.   How about this?  Why can't I just e file my entire 2018 tax return.  Then separately simply mail the election using form 8453.  Kinda like the situation here: https://ttlc.intuit.com/questions/4400974-i-have-already-filed-my-2017-return-but-want-to-make-a-mar...

Is that okay to do?

[Ponygrrrl]

As long as you follow the rules stated by the IRS and have already filed an extension, you can elect in TY18.  Otherwise you will have to wait.  In general late 475(f) elections are not allowed.  See instructions under Mark-to-Market Election heading here.