SMTP is a wonderful protocol that queues messages and retries delivery for 5 days so a non-responsive email server is no issue. Just do not have a temporary solution that bounces emails since those will never arrive (the sender is notified about the bounce).
Marcus On 03/01/2023 21:31, Bruce Johnson via bind-users wrote:
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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