Getting rid of an obsolete email that is blocking my new account?

Are you using Send Email from the Acrobat toolbar?

• If you opt to use the default email application in the Send Email dialog box that appears, it will use the email address that is set as the default email address in your email application on your computer.
• To change this refer to your email application user documentation.

For example if you are using Microsoft Outlook:

1. Click on the File tab.
2. Click Info, then select Account Settings.
   
3. Select the email account that should be used as default in the list of email accounts.
   
4. Click Set as Default, then click Close.
5. If you now try to send an email from within Acrobat, it should default to the selected email address.

No directly related to the possible issue you describe, but something you might also want to update is your Identity settings in Acrobat preferences (these are used for other purposes, e.g. using Comments etc.).

1. Choose Edit > Preferences
2. Click on Identity category on the left
3. Update your Identity as well as the email address.