[ILUG] Very elementary question on email

[Timothy Murphy]

Story: yesterday I resuscitated a Sony PictureBook (C1VFK)
which I thought had been dead for over a year,
and which I was about to send to a re-cycling grave.
(I opened it, blew on the works with compressed air
and sprayed the contents with contact cleaner.)

Then I installed Fedora 7 (this took 14 hours)
and to my amazement it seems to be working perfectly.

But my query is - why is email working OK,
despite the fact that I didn't do anything to sendmail.mc (or .cf)?
How does the email know where to go?
I have connected the machine by ethernet to my LAN,
and was surprised that that worked without any steps on my part,
despite the fact that /etc/sysconfig/network-scripts/ifcfg-eth0
was completely wrong.

What exactly is the story of an email message?
I realise it is sent out through port 25,
but is that sufficient?
Is it up my ISP (Sir Anthony) to forward it correctly?

I've always gone to great trouble to specify the mail server
(in my case smtp.eircom.net)
but it seems that is unnecessary?

I tried to follow a test message with tcpdump and wireshark/tshark,
but that proved impossible as both stopped the connection.