Mail on Holiday / Out-of-office Auto-Delete Rule

Wow. What a lot of opinions.
I was thinking of asking the same question, but looking at all the opinionated answers, I'll carry on googling.
And since I do have 5 minutes to spare - yes, it's a behavioural issue, and that's EXACTLY why you use tech to assist it.
If HR sets a policy to say "Don't email a colleague who's on holiday" and people still do it, yes you could fire everyone who contravenes, yes you could start disciplinary actions, yes you could reduce their bonus, yes you could report it to their managers, yes you could pay a consultancy company to deal with the behaviour issue and/or the cultural change, yes you can send reminders on a regular basis...

OR

You can just do an auto-reply "the colleague you've tried to email is on holiday as you've seen from his out of office, therefore, as per HR policy your email has been deleted".

Simples.