Email migration and MX records

[E R]

Bruce, I would push back and ask for more information from whomever is
leading you down that path as it does not sound right to me although others
more familiar with DNS magic might have better suggestions to DNS changes.
But if Barracuda is just a front-end for email that does antivirus/spam
filtering I would expect you could update Barracuda to send email to your
new M365 tenant when it is ready without any DNS change to your MX record.
Once that change was made you could then update MX records to bypass the
Barracuda service altogether.  Keep in mind that you may specify a short
TTL, but you may see emails for DAYS after the change from my experience
when we changed our MX servers years ago.

If you received information that you could not use a third party device in
front of M365, you received incorrect information.  You can definitely use
another service in front of M365 although the additional cost might not
pencil out.  We let the third party store dangerous/nasty emails in their
quarantine and forward SPAM/Bulk over to M365 Junk Email folders so
employees have one space to look for those things.

>
> -----Original Message-----
> From: bind-users [mailto:bind-users-bounces at lists.isc.org] On Behalf Of
> Bruce Johnson via bind-users
> Sent: Tuesday, January 3, 2023 3:32 PM
> To: bind-users at lists.isc.org
> Subject: Email migration and MX records
>
> We?re making an O365 tenant switchover for our domain (a subdomain of the
> arizona.edu domain) and moving from our Barracuda cloud email SMTP to the
> University?s tenant, but email cannot flow until the Arizona.edu O365
> tenant can take over our email domain.
>
> In anticipation I set our TTL for MX records quite low before the break
> (150 seconds) so, but the process may take up to an hour (if everything
> goes well )
>
> Will setting our mx record to a bogus address cause email to bounce on the
> sending end and eventually get retried later after the mx record has been
> properly set to the Universities main smtp MX address?
>
> Or are we approaching this in the wrong way?  Basically our end result is
> we want to stop accepting email from anywhere until the whole process has
> been changed and we have established the correct route so email starts
> flowing correctly.
>
> As it?s been explained to me the main campus tenant cannot start accepting
> email for our domain  until we?ve transferred the email domain between
> tenants, so we cannot just change the MX record in our DNS server to the
> University?s (a Cisco Ironport setup)
>
>
>
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