New SMTP and old SMTP + Drop old SMTP but respond with custom message to external recipient + a lot more (Revised)

Maybe I'm just missing something and need a second pair of eyes but I've looked at Rights Management, Compliance and Security, SPAM, basically anything that will allow me to create a "profile" for a precise domain name and when someone@domain.com sends to my customer they get a professional response back that says "Hi, we had to change our email domain and we are now this if you have any questions give us a call at this".  But the intended recipient cannot get the email, yet I would like them to get notified so they can reach out if necessary and I want to create a report or generate a report when they as or I want to know is what I did doing its job like I said it would do.  Transport rule won’t do this, why?

I know how to do this with simplest approach but I'm hoping to do better than what I have for options such as Transport Rule and a very limited response ability with Exchange or in this case Exchange Online.  I have a customer where I'm presently in the middle of an Office 365 Migration.  Hybrid Mode.  52 registered domains.  One Tenant.  One business unit in that tenant is domaina.com and due to litigation reasons cannot use that domain starting in one week but the agreement reached is they could keep the domain registration and managed DNS until year end.  This is important to keep the MX record pointing to Exchange Online so we can let external customers know to update their first.last@domainA.com to first.last@domainB.com

But, none of that mail can get delivered.  Only dropped and a response back which my customer wants to look something like this:

Your email was not delivered. The email address you are trying to reach has changed. Please update the contact email to reflect our new domain, domaina.com, and resend your message.

For example, if you are trying to reach john.doe@domainA.com, the new email address is now john.doe@domainB.com.

If you have any questions, contact our office at (866) 555-5555

Which I agree is more professional and should be possible, by now.  And given all the tools I have with Office 365 and this customer having E3 licensing, Azure Premium, Intune and so forth I'm hoping to meet this deliverable as asked but would like to bring additional value if possible.  I would like the mail to terminate at the tenant, deliver that message above, and extrapolate out the sender information and forward a notification to the original intended recipient that they received a mail from XYZ and in a professional style that makes the customer feel all warm and cozy because I feel this brings additional value add.

I'm always looking to improve or prove the value of technology or perception of technology.  The transport rule gives me a lot of options, not complaining.  I can do this simply with a transport rule - not sure about the last item to notify the customer - but that field to reply is limited to 4096 characters?

There must be a way to pull this off but where the mailbox already resides in the cloud.  I think there are third party tools out there for on-prem but this mail never goes to on-prem.  I have a third-party cloud provider in front of incoming mail.  There are other third-party providers that I can put in front of Office 365 or Exchange that are cloud or appliances on-premesis that I would be interested to know of the ones that could do all what is requested above – but doesn’t help right now.  

So, that is not an option to use that where it comes in initially then hits 365 Cloud, then the mailbox in the cloud.

Outlook autoresponse for entire domain is not an option although if I had that functionality in Exchange Online it would fix that 1st issue with the professional response in Outlook format email response.

Basically CodeTwo Exchange Rules but for Exchange Online, but better.  And custom reporting that I can generate automatically to myself and the managers of that entity how well we are doing our job.

I've googled and cannot seem to hit the right combination of keywords.   Forums.  Blogs.  Powershell options where somethings things are “hidden”.  

Of all the things that must be accomplished to add a domain to an Exchange Organization, with AD and Exchange On-Prem but running in Hybrid-Mode, mailboxes already migrated to the cloud, new UPN, new SMTP alias, domain registration, managed DNS, adding the domain to Office 365, TXT records, SRV records (Skype for Business), then swapping out the existing primary to secondary, taking the secondary of first.last@newdomain.com, and on set date except mail from original primary SMTP domain, don’t deliver it, drop it, respond with a message.  I have most of that scripted.  That is the easy part.

So, in full transparency I am looking to improve that process and create more value for my customers.  It just makes more sense to me that you should drop the mail, send a notification that is not NDR but a message that the domain has changed instead of something generic giving false impression that user has been fired, instead a customer message providing correct information then notifying the intended recipient “we got this just letting you know, signed… IT”, automated report end of day to all the managers saying “we got this, just letting you know, here is what happened today.  Signed IT” – is my minimal standard?  

If it doesn't exist, it should - IMO.  If it were not an obvious value add, I would not put it in writing and ask.  

If this does exist, great.  If it doesn’t, maybe we can use this opportunity to make it exist and I’ll reward points accordingly.