I have a lookup column that lets the user choose a Person. That person then gets emailed via a button in another column. After this email has gone out, I need to make sure that Person doesn’t get changed.
To accomplish (almost) this, I’ve set the filter on the lookup column options such that the only option you can choose is the option that was already there. So you can’t change the person.
Trouble is, the user can select Blank which messes things up. Is there any way I can disallow Blank as an option in a lookup column?