There are two possibilities.
You can keep the old Adobe account, but change the email associated with it.
That is what you need to do if you have bought books that you want to continue to read.
To do that, go to the Adobe web page and sign in using your old email.
Then go to My Adobe (top right) and My Adobe ID (near top left under My Information).
There you can change the Adobe ID associated with the account, and hit 'Save Changes'.
This won't change the authorization of the PC to the account.
It might still give the old email for a time if you query authorization;
but it is the account that is important, not the email it is currently registered to.
To be extra sure, you can deregister [ctrl-shift-D (cmd-shift-D on Mac)] and reregister, as below.
The old email is just an identifier, it doesn't matter that it is no long valid.
Unless you have forgotten the password, in which case you won't be able to use standard password recovery.
If you need the old account and have forgotten the passsword and no longer have access to the email account,
you must contact Adobe to get it all setup again.
You can create a new Adobe account for your new email.
This may be easier if you only use library books and don't need access to any DRM books registered to the old account;
especially if you have forgotten your password.
For a new account, once you have signed up for the new account at the Adobe website,
use ctrl-shift-D (cmd-shift-D on Mac) to ADE (Digital Editions) to remove the old registration.
Then go to menu/Help/Authorize Computer (Library/Authorize Computer on the older more reliable v1.7.2) and authorize with your new ID.
As you informed that you do not have access to the old email address, not to worry, in this case, if you have ebooks downloaded on your system, first you need to contact your ebook vendor and ask them to change the email address from old email address to a new email address [ Please note here, the new email address to which you are about to change must not have an account registered with Adobe , it should be an unregistered email address with Adobe ]. Once the Ebook vendor changes the email address from old email adderss to new one, you will have to contact Adobe customer service and they will help in changing the email address of the Digital edition from old to new.
Once this is done, all the Ebooks will now be under your new email address.
After which you will need to deauthorize your device and reauthorize so that your new email address is recognized by the device, for which follow the below steps:
[ In Adobe Digital Edition (ADE), if you press Ctrl+Shift+D (Windows) or Cmd+Shift+D (Mac) will remove the activation on your computer, and allow you to reactivate with a different ID or the same ID when you launch ADE again. ]
Press "Ctrl+Shift+E", this will bring up the "Device Deactivation" dialog.
Select your Reader and deactivate it.
Unplug and replug your Reader
The Device Authorization dialog should show up, and you can authorize again with your Adobe ID.
In case if you face any issue with the deauthorization and reauthorization, you can contact adobe chat support at [ https://helpx.adobe.com/contact.html ] during the business hours, Monday to Friday and your issue will be resolved.