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Re: Email tutorial?

On Tue, Apr 24, 2018 at 04:44:24PM -0400, Greg Wooledge wrote:
> On Tue, Apr 24, 2018 at 04:25:56PM -0400, mark@xxxxxxxxxxxx wrote:
> > DHCP is like that, with an added twist:  When IP address change, in order for 
> > you to get the e-mail an association between your IP-address and your physicla 
> > computer, the change has to be broadcast to all the IP servers on the Internet 
> > before you will be able to receive mail again.  That change can take days.
> I know it's just an analogy, but this part is a bit misleading.  DNS
> entries have a configurable "time to live" field, measured in seconds,
> which tells caching DNS resolvers how long they're allowed to keep the
> old addresses in memory before they have to check again for a changed
> address record.

There is a caveat tho.
Email is slow and stubborn (at least most implementations are).
Once the server determined the MX record (which has to be a host btw) it
sticks to it. Even if the address of the host changes.
So that time required to update that MX record can screw up things.
And it is actually not the TTL which is critical here it is the time
you need to update the DNS records + the TTL.

Just saying.


Henning Follmann           | hfollmann@xxxxxxxxxxxxxxx