Let me try to spell it out.
ebay.com is their domain
Some of their pages have
my.ebay.com or
search.ebay.com
these are sub domains
They might be a differant server but they are all part of ebay.com
After the domain (ebay.com) is the address of the page
This could be a long URL like:
http://cgi6.ebay.com/ws/eBayISAPI.dll?MfcISAPICommand=ViewListedItems&since=30&userid=sailorpatp&include=0&rows=200&sort=3&completed=1
The point I am trying to make is all of their pages are at ebay.com not ebay.somethingelse.com
The name right in front of .com has to be ebay or it is a spoof site.
In a email the link might look like the right address but the site that is behind the link is not the same address as the link looks like. This is done by writing a bit of HTML code that is not hard to do. I could show you in a email but the code would not show on this board.