Update field from #__users

Is there a way to use auto actions to populate the users email address from #__users to an email field [cb_email] on user login?

Yup, but why are you needing a copy of the email address in a second field? You should be able to just use a [FIELD_NAME] substitution for email anywhere that supports substitutions. Example as follows on how to copy 1 field value to another on login.

Global
Triggers: onAfterLogin
Type: Field
User: Automatic
Access: Everybody
Action
Field: Email
Operator: Set
Value:
You may also want to add a condition so it's not saving the user object on every login. Example as follows.

Conditions
1: [cb_email] Not Equal To

Thanks! I knew how to do it... should have followed my instincts and tried it. The reason for the second field is that I wanted to display this on a separate tab that is only visible to moderators. I also wanted to display the email address and not just a blind link to email them.

Since you only need it for display purposes I suggest just using a Custom HTML field with the below substitution.


You then won't need to deal with storing it twice.