Interesting request for Exchange rule. Not sure if I know how or if I can do it.

I see a lot of naysayers; this isn’t a simple task but it is do able with the right know how.   I would say 1. Convert Old to a shared mailbox.  Pull the old email alias off the Old mailbox and replace it with something like “xxOld@domain.com” 2.  Assign Old@domain.com to New and then make New a full access delegated admin on Olds mailbox. 3. Set up a power automate flow under News account.  Have it be something like - Email received with the address “Old@domain.com” > create an email to send to the sending account with the introductory email.  This is really super vague but the general premise with what you actually build will at least follow this logic. 4. bonus points so you don’t spam people- create an excel file somewhere the power automate flow can read > whenever the flow sends an email to someone, have the flow append the excel file with the email address it just sent to > before the flow sends the email, have it check that excel file for the presence of that email and then have it skip sending the email so it doesn’t constantly resend emails.   At the end of the day this is fairly complicated to do, and will likely take a couple hours to make sure it works properly- is your time more or less valuable than the new sales guy?  But I think it’s important to think creatively about how the solution could be solved, just to entertain his idea and then even show him why it wouldn’t work.  You could probably set this up with a no code flow solution like Zapier which will probably be easier to set up, but have other restrictions.   Probably NOT worth the effort, especially when he could do something like…. Take the contacts from Old and just mail merge an introduction to all his contacts- or you can repurpose his Autoreply to be News introduction mail.  Lots of ways to skim this cat tbh.