Hello.
It really depends on your mail volume and the reliability of your
primary MX hostname. Typically the RFC permits mail to be delayed for up
to 5 days at which mail will bounce back as undeliverable. For most
low-volume sites, a primary only MX configuration is fine.
Both of those domains have either Round-Robin DNS or multiple MX servers
which provide a similar function.
outlook.com mail is handled by 5 outlook-com.olc.protection.outlook.com.
outlook-com.olc.protection.outlook.com has address 104.47.14.33
outlook-com.olc.protection.outlook.com has address 104.47.13.33
Yahoo has multiple server weight 1 servers providing redunancy.
yahoo.com mail is handled by 1 mta6.am0.yahoodns.net.
yahoo.com mail is handled by 1 mta5.am0.yahoodns.net.
yahoo.com mail is handled by 1 mta7.am0.yahoodns.net
Thanks
Matthew
On 5/22/2023 6:53 PM, Tom Reed via Postfix-users wrote:
PS: Why do you (think you) need a backup MX?
Hello
I am not sure why I need a backup mx indeed, but if you make a simple dig,
you find gmail, fastmail, protonmail, comcast, free.fr those big providers
do have backup MXs.
Though yahoo, outlook don't have backup MX as a comparison.
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