Re: Permanent email address?

[Greg Wooledge <greg@wooledge.org>]

On Tue, May 17, 2022 at 12:20:52PM +0100, mick crane wrote:
> On 2022-05-17 01:44, rhkramer@gmail.com wrote:
> > Thanks to all who replied!
> > 
> > I'll need to think over what I want to do.
> > 
> > I guess if I want to run a local MTA, I'd need either a static IP
> > address
> > (along with a domain) or I'm guessing I could use one of those services
> > (and
> > software) that lets you use a dynamic IP address (by doing something
> > like
> > updating you if your IP address changes.
> 
> I think the way it worked was the dynamic ip people gave you namespace
> within a domain that they control then monitored your ipaddress from your
> ISP for changes and redirected requests to your name in their domain to
> that.

... no.

The way dynamic DNS works is: every time your public IP address changes,
*you* detect that it has changed (via some sort of automated process),
and *you* report the new IP address to the dynamic DNS provider (again,
this is automated).

So, the pieces in this puzzle are:

1) You need a dynamic DNS provider.  This may be free, or not.

2) You have an account with said DDNS provider, typically with a password
   or something, so that only you can report changes to your IP address.
   Your reporting process has to be configured to send your account
   information, including password, along with the new IP address, using
   whatever means are indicated for your DDNS provider.

3) You need a way to know when your public IP address has changed.  If
   your machine is directly on the Internet, this is easy -- you can
   simply set up a hook in your DHCP client configuration.

   But more likely, your machine is on a private non-routable network
   behind a NAT router, with the SMTP port forwarded from the router
   to the internal machine.  So it's the *router's* public-facing IP
   address that you need to know has changed.

   Some routers have built-in dynamic DNS reporting capability -- in
   other words, the router itself might be configurable to report your
   public IP address to a dynamic DNS service provider.

   If that's not the case for you, that leaves polling.  Every x minutes,
   poll to find out what your public IP address is.  If it has changed
   since the last poll, then report the new IP address to the DDNS provider.
   You might be able to poll the router itself, via some sort of web
   interface.  Or, more likely, you might poll some external web site
   that exists to tell you what your public IP address is.  There are
   many of these.