Suppose that hostname gives hostX. hostX doesn't exists in dns nor in /
etc/hosts (it's unresolvable).

Now when trying to connect to smtp service:
>>> import smtplib
>>> smtplib.SMTP('akcyza.pld-linux.org')
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/share/python2.4/smtplib.py", line 255, in __init__
socket.gaierror: (-2, 'Name or service not known')

The problem is gethostbyname() here:
                 # We can't find an fqdn hostname, so use a domain literal
                addr = socket.gethostbyname(socket.gethostname())
                self.local_hostname = '[%s]' % addr

It's much easier and better to just use getsockname() for local socket. 
Attached patch fixes this problem and doesn't require for the local 
system to be resolvable in dns/hosts.

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Why would getsockname return '0.0.0.0'?

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On unconnected socket it returns 0.0.0.0 afaik which doesn't happen 
here. Please drop that part.

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Patch is wrong btw. Doesn't allow to create pure object 
without connecting.

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Maybe just always fallback to safe value?

--- Lib/smtplib.py.org  2006-03-31 20:57:05.000000000 +0200
+++ Lib/smtplib.py      2006-03-31 20:57:28.000000000 +0200
@@ -255,7 +255,11 @@
                 self.local_hostname = fqdn
             else:
                 # We can't find an fqdn hostname, so use a 
domain literal
-                addr = socket.gethostbyname(socket.
gethostname())
+                addr = '127.0.0.1'
+                try:
+                    addr = socket.gethostbyname(socket.
gethostname())
+                except socket.gaierror:
+                    pass
                 self.local_hostname = '[%s]' % addr

     def set_debuglevel(self, debuglevel):

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Committed safe patch in rev. 43499, 43500.