Can I find out with just an email address the identity of the sender??
This could be a case of stalking and inappropiate dialog.

Dear Poppet,  

Hate mail is a violation of laws, and matter to the police and to the
ISPs (Internet Service Providers).  Hate mail and hate language are
not a funny thing and you shouldn't be handling that on your own - you
should let professionals handle it. There have been cases whereas hate
emails were the first step towards much more violent acts and in
general, it is not different from stalking and its possible dangerous
consequences.

Referring specifically to your case, email users can enter whatever
data they want in the registration boxes of Hotmail and other free
web-based email services. 
 
Email address contains an alias that the client chooses (for example
"name") and the service provider on which the email is stored. For
example: "name"@yahoo.com or president@whitehouse.gov (the US
President's email).

In the first case, the person could remain anynymous: they could
register as "john doe" of 12222 st. in New York. The email service
provider itself doesn't know who the client is, only how they call
themselves, and which server they are using (although this detail
could be also masked by professionals).

In the second case, you have the work place of the intruder, as well
as his alias in this place, and this is much easier to find, if the
identity in the email has not been forged.

Email identities could be forged. If you ever receive spam, and click
on "view full headers" instead of just erase it, you'd see that most
spammers forge several addresses, and go through several servers.

The first thing you should do is to check, whether this person really
sends you the mail from the email address it seems he does, or is that
only a route, and alias. You do that by choosing to view "full header"
of the email. You can read an explanation of how it works here -
http://www.emailabuse.org/sender.asp and then a "how to" guide on how
to do this here: http://spamcop.net/fom-serve/cache/19.html (by
systems).

After you do tat, contact the service providers of the stalker: the
original one, as well as those who appear in the full header (if there
are any). Forward them the hate mails as they are (only with full
headers) to mailto:abuse@hotmail.com
 
Reporting abuse can be also done here -
http://www.emailabuse.org/report.asp and more abuse reporting tools
can be found here - http://www.abuse.net/
 
Another possibility is to report the abuse to www.spamcop.net SpamCop
- they'll continue for you and might virtually nick the person behind
it.
 
In the UK, hate mail is an act investigated by the police (see for
example http://news.bbc.co.uk/hi/english/uk_politics/newsid_1182000/1182370.stm
; http://news.zdnet.co.uk/story/0,,t269-s2085114,00.html).
 
You should also consider contacting the police. Therefore, in order to
file a complaint and to succeed in it, you must maintain documentation
of the hate mail (incl. headers, etc.). Whether to contact Hotmail or
the police first is a tactical question: if you contact Hotmail first,
they might just block this person's email address, and he might move
his "business" elsewhere without stopping to harass you.
 
There are also sites and support groups that deal directly with the
problem. For example, http://www.emailabuse.org/default.asp 

http://www.onlineharassment.com/ This FAQ (frequently asked questions)
deals with all sorts of abuse - like Spam, harassment etc.

http://members.aol.com/emailfaq/emailfaq.html

I also add my search terms, that might help you:  
"hate emails" "criminal law" uk  
"hate emails" "criminal act"  
"hate emails" fighting  
"stopping hate mail" (no results) 
"reacting to hate mail" (no results) 
"responding to hate mail"   
"full headers" spam 
"hate mail" 
protection against "hate email" 
"hate e-mail" OR "hate email" OR "hate e-mails" OR "hate emails"
(notice how many result this gets -
://www.google.com/search?q=%22hate+e-mail%22+OR+%22hate+email%22+OR+%22hate+e-mails%22+OR+%22hate+emails%22&btnG=Google+Search&hl=en&lr=&ie=UTF-8&oe=UTF-8
- which says something about the spread of the problem)
"hate emails" spam  
"hate email"  
related:www.emailabuse.org/
(://www.google.com/search?q=related:www.emailabuse.org/&hl=en&lr=&ie=UTF-8&oe=UTF-8&start=20&sa=N)
"email abuse" "hate mail" (the most fruitful for this answer:
://www.google.com/search?q=%22email+abuse%22+%22hate+mail%22&hl=en&lr=&ie=UTF-8&oe=UTF-8)

I hope that answered your question. Please contact me if you need any
further clarifications on the answer. I'd be pleased to clarify my
answer before you rate it.

Firstly, the email address contained in the "From" and "Reply-To"
headers of messages can be completely unrelated to the actual sender,
as these lines can be easily faked.

You would require the full headers of the relevant messages. At some
point this will usually contain the original sender's IP address,
which will take you to his ISP. You are then dependent on the ISP logs
being able to identify the sender, which will depend on both the
quality of logging run by the ISP and the quality of any identity
verification carried out by the ISP on its customers. IP addresses can
also be falsified. However, most people aren't that technically aware.

There is an excellent article about tracing the senders of emails (in
this case, for mail bombs ie malicious bulk mail) at:

http://www.reagoso.com/inet/IAB_MailBombs2.htm

Finally, more and more police forces are becoming aware of Internet
related crime and have specialist staff able to carry out
investigation.

I hope this helps

Owain