Swapping between main & secondary ISP for our mail server


We currently have 2 ISPs & are using primary & secondary mx records for the same server - pointing to mail.ourdomin.com & pointing to mail1.ourdomain.com - both addresses are on our firewall which in turn forwards the relevant mail ports to the same one mail server's internal IP.

I'm supposed to swap between the 2 mx records so that the primary is secondary & vice versa (at the end of the year we'll stop working with the primary ISP, but for now both addresses are still operational).

1. Am I to expect a long downtime with sending & receiving emails? if so is it going to be the 24h to 48h of the mx change or will servers around the world still be using the old records they have & everything is expected to work till the swap actually take effect?
2. Am I required to do anything in addition to changing between the primary & secondary mx records with my domian's provider (Network Solutions)?

Thanks in advance!
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DeepinInfrastructure Engineer Commented:
MX records are propagated a lot quicker nowadays within the hour but some servers still take up to 48 servers to show the correct records, you should consider planning it for a Friday night give the whole weekend to propagate

If you have a managed spam filter message labs etc- worth changing the priority orders so secondary will be first
meirgilAuthor Commented:
Thanks for the quick response!
I'm wondering if there's a reason for a down time at all - both addresses are still active, it's just that the primary will be secondary & the other way around..
Will servers around the world sending & receiving emails care which one is primary & which is secondary & refuse emails from/to my server?
DeepinInfrastructure Engineer Commented:
No there shouldn't be as you said both are active

doesn't make a difference to servers around the whole, only your firewall would refuse if port forwarding is not in place, but as its a secondary line - im sure that's already been checked?

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meirgilAuthor Commented:
Yeah, Thanks Deepin! Firewall configured to forward the ports.

I have then a second question, not sure if it's ok to have it still inside this thread but here goes:

The second stage will be swapping between the server's names so that will change to mail.mydomain.com & will change to mail1.mydomain.com.

Am I correct to think what I need to do is as follows:

1. Request both ISPs to change the Reverse DNS records they have to reflect the change.
2. At the same time change the IPs at the mx records at Network Solutions' website (bought the domain name from them).
3. Change the A records at Network Solutions'.

4. Do I need to reissue a new certificate for my Exchange 2010 server from Digicert? (bought the certificate from them).
5. Change the record in our own DNS server.

Anything else? Am I right with the steps? Anything I should note before going ahead? Downtimes?

Thanks in advance!
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