A common configuration is that email destined to addresses "inside" the organization does not require authentication, while "outbound" email does require authentication. This allows an organization to receive inbound email while not becoming a source of spam sent by unscrupulous random people on the internet.
This is often implemented by having completely separate sets of servers responsible for inbound and outbound email. Outbound servers are configured to require authentication in all cases, while inbound servers do not require authentication but will only accept messages destined for delivery inside the organization.
I queried for the MX of googles mail servers and tried initiating SMTP
session via telnet, but it didn't seem to work, I just had a black
screen, no HELO, no EHLO, nothing.
This seems to work as expected.
$ host -t mx google.com
google.com mail is handled by 30 alt2.aspmx.l.google.com.
google.com mail is handled by 20 alt1.aspmx.l.google.com.
google.com mail is handled by 10 aspmx.l.google.com.
google.com mail is handled by 40 alt3.aspmx.l.google.com.
google.com mail is handled by 50 alt4.aspmx.l.google.com.
$ telnet aspmx.l.google.com. 25
Connected to aspmx.l.google.com.
Escape character is '^]'.
220 mx.google.com ESMTP db10si2487268vdc.138