[ds9]

I wonder whether it is also a bad practice to set the contact email to an address on one of the domains that that registrar controls. I.e., register example.com with DomainCo, and your contact is [e-mail]?

I actually do this and am considering changing the contact email for registrar 'A' to something independent of 'A'.

It does seem hard to have enough confidence in the reliability of any email address.