On Tue, Sep 14, 2021 at 08:24:00AM +0100, Nick Howitt <n...@howitts.co.uk> wrote:
> On 14/09/2021 04:29, raf wrote: > > > > On Tue, Sep 14, 2021 at 01:20:03PM +1000, raf <post...@raf.org> wrote: > > > <snip> > > > > But chances are that mail clients just do what any > > other TCP client would do. That might be why you can't > > find any discussion on the topic. Remember, the only IP > > address(es) that the mail client will be concerned with > > is that of its smarthost. In most cases, that will be > > an ISP that only has to deal with its own customers, > > not the whole planet, so there will usually only be one > > IP address (or one per region). So the mail clients > > might not have ever needed to put much thought into it. > > > > cheers, > > raf > > > Big assumption based on one example of gmail.com. Try outlook.com: > > [root@server ~]# dig -t a outlook.com > <snip> > ;; ANSWER SECTION: > outlook.com. 120 IN A 40.97.128.194 > outlook.com. 120 IN A 40.97.161.50 > outlook.com. 120 IN A 40.97.164.146 > outlook.com. 120 IN A 40.97.148.226 > outlook.com. 120 IN A 40.97.160.2 > outlook.com. 120 IN A 40.97.156.114 > outlook.com. 120 IN A 40.97.153.146 > outlook.com. 120 IN A 40.97.116.82 > <snip> Yes, that is a mail service provider that does need to service the whole planet, unlike many ISPs. And perhaps ISP-based email accounts are less common than they used to be. It would make a good target for testing what a mail client does when sending mail if its source code is inaccessible. cheers, raf
