On Tue, 26 May 2009 11:03:59 PDT, gb10hkzo-nanog@yahoo.co.uk said:
would be most interested to hear NANOG theories on the variety of MX record practices out there, namely, how come there seem to be so many ways employed to achieve the same goal ?
The trick here is that it isn't always *exactly* "the same goal". There's multiple mail system architectures and design philosophies. One often overlooked but very important design point for the *large* providers: % dig aol.com mx ;; ANSWER SECTION: aol.com. 2805 IN MX 15 mailin-01.mx.aol.com. aol.com. 2805 IN MX 15 mailin-02.mx.aol.com. ... ;; WHEN: Tue May 26 14:40:41 2009 ;; MSG SIZE rcvd: 507 That 507 is critically important if you want to receive e-mail from sites with fascist firewalls that block EDNS0 and/or TCP/53. 5 bytes left. ;)