How to disable vbulletin sending e-mails to a certain user?

[postcd]

Hello,

i am receiving "Undelivered mail returning to sender" e-mails from time to time:

550 5.7.1 <member@email.here>: Recipient address rejected:
Recipient not found (in reply to RCPT TO command)

my hourly mail quota is limited so rather than trashing these e-mails i am trying to disable e-mail sending to such user in admincp

Editing user profile, this NOT helped:
- Receive Admin Emails (No)
- Users Awaiting Email Confirmation (ticking the tickbox)

My other non-tested/non verified ideas are:
- ban user (not ideal, not good for user, time consuming to ban and mention the reason)
- remove user e-mail address entirely and add to group Pending email confirmation (so user see message set for this group to explain that they need to change e-mail.)