Look at it this way, anywhere that has resolvers forwarding to other resolvers 
that forward to yet another set of resolvers before the query gets to the root 
servers (anywhere with a complex network and multiple layers of firewalling) 
will have a succession of caches that need to clear .. so might take somewhat 
longer than whatever TTL you set.  The recommendation therefore is to lower the 
TTL for a few days BEFORE you change your DNS records.

--srs
________________________________
From: NANOG <nanog-bounces+ops.lists=gmail....@nanog.org> on behalf of Laura 
Smith via NANOG <nanog@nanog.org>
Sent: Saturday, August 10, 2024 7:46:31 PM
To: nanog@nanog.org <nanog@nanog.org>
Subject: Any ideas how long gmail cache DNS records ?

In typical "Google knows best" style they appear to be ignoring SOA and TTL and 
doing their own thing.

Changed DNS severs and MX records, other public mail services have picked it up 
no problem.

Gmail however appear to be insisting on continuing to deliver to the old mail 
servers for god knows how much longer ?

Any ideas how long I can expect this to go on for before they Do The Right 
Thing (TM) ?

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