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exchange dialup


I have my firewall (linux) configured for broadband with failover to a dial-up modem to an ISP on a local call rate.
Should the broadband fail, the modem connects to the internet fine and exchange sends email fine as the local gateway is still the same.
Howerver I would like to be able to receive email - any ideas what the best way forward? Can exchange be configured to collect SMTP email from an ISP but not using POP/IMAP ?

Thanks for pointers, I am used to the broadband world where I get static IP addresses, etc !


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8/22/2022 - Mon

The problem you have is DNS replication. Any change takes 48 hours to fully propagate.

What you could do is use a dynamic DNS service.
Configure a dynamic DNS account and install an update tool on to your Exchange server. That will keep the IP address up to date with them.
Then add the dynamic DNS address (yourname.dyndns.org) as an additional MX record to your DNS, with a higher value.
While your broadband is alive, the IP address will match your live address (so both MX records ultimately point to the same place), but when it fails, the dynamic DNS service will update with the dial up service IP and 15 minutes or so later, email will come in.
When the broadband comes back up again, the dynamic DNS update tool will change the IP back to the real address and email will come in the other way as normal.

That is presuming of course that the dial up service allows inbound SMTP.

If it doesn't, then you need to find a backup mail service that supports ETRN. ETRN is basically SMTP on demand, so your Exchange server asks the remote server for any email.
You would need to run that all the time as the backup server would have to be in the MX records for the failover to happen automatically.


Hi Simon >> Could I configure an exchange server to support ETRN? If so I could exchange services with a friend's company which could also make use of this feature - we could use each other for fail over ?

You can use another Exchange server to do ETRN.
However, I wouldn't configure it so that it is in the MX records all the time as that will lose recipient filtering and other features.


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Ok thanks this outlines how to setup an exchange server to hold mail for another domain - back to the original problem, on a dialup modem how could I configure my main echange server to force the ETRN method to get the email which is being stored ion the other exchange erver without waiting for the main broadband to come back online again?

Sorry if this is too cryptic!

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ok thanks for the guidance, I do not have time right now to test this but will do in the forthcoming weeks