Email Address
Due to security precautions, it is not possible to change the email address that was used to create your account at the time of registration.
If you have access to the email you'd like to switch, simply create a new Poloniex account and transfer your funds from the original account to your new account.
Well, that's the current version of the TOS. The account was created 19-October-2016 at at 21:31 CET. The TOS at account creation time was this:
https://web.archive.org/web/20161008181523/https://poloniex.com/terms/.
There is nothing in there that the Email address assigned to an account cannot be changed.
I totally understand under security aspects that they are denying to change the assigned email address if the owner cannot proof the ownership. But they are not even have a process to do so and explicitly exclude this in their current version of the TOS. BTW: the quote above wasn't even in written in the
TOS version 21-January-2020.
They are not changing TOS, they are just updating it which means every user who created accounts before the change of ToS should agree the terms for continuous usage, so you can't argue with poloniex with this point.