***Account-related emails, such as Account Activation and Password Reset, are exempt from Unsubscribe Preferences for Active and Pending Users, as they are required for account maintenance. ***
Email notifications and Reminders sent by Channeltivity include an unsubscribe link that allows the recipient to quickly turn off all emails sent by the portal:
Unsubscribing puts their address on the "Unsubscribed Email Addresses" list and blocks all further messages, with the exception of Password Reset and Account Activation emails. You can find this list by logging in as an Administrator and going to Settings > Portal Configuration > Unsubscribed Email Addresses. You can remove recipients from the Unsubscribed Email Addresses list by checking the box and clicking the "Delete" button. All actions are logged and can be found on the User's profile.
How Can Users Manage Their Email Settings/Preferences?
Users can update their Email Settings to choose whether they want to receive emails by going to their User Profile in the top right corner of the portal > Email Settings.
Click the "Actions" button in the top right > Update Email Settings.
Uncheck the "Subscribe to Receive Emails" checkbox to unsubscribe from all email notifications with the exception of account-related notifications such as Password Reset and Account Activation Emails.
System Admins can also edit a User's Email Settings by going to Admin > Users and clicking on the name of the User whose Email Settings they wish to update. They'll then click the "Actions" button in the top right of the User's Details page > Update Email Settings. 
Related Documentation:
How Do I Update My User Email Settings/Preferences?
What Email Notifications Are Available?