Validation emails possibly malformed

When email validation is enabled in preferences->registration, XWiki spits out the following error when a new user attempts to register:

Error number 10005 in 10: Could not login to mail server mail.xxxxx.net port 25 error code 501 (501 5.0.0 Invalid domain name ) com.xpn.xwiki.XWikiException: Error number 10005 in 10: Could not login to mail server mail.xxxxx.net port 25 error code 501 (501 5.0.0 Invalid domain name )

Also see this related question regarding sendmail and XWiki:
http://mail-archive.objectweb.org/xwiki-users/2005-10/msg00039.html

The problem seems related to the XWiki HELO when initiating the transaction with the sendmail server.
It is sending HELO XWiki <sp> <VersionInfo> instead of HELO <domain>

The SMTP RFC states the following (http://www.faqs.org/rfcs/rfc821.html):

3.5. OPENING AND CLOSING

At the time the transmission channel is opened there is an
exchange to ensure that the hosts are communicating with the hosts
they think they are.

The following two commands are used in transmission channel
opening and closing:

HELO <SP> <domain> <CRLF>

QUIT <CRLF>

In the HELO command the host sending the command identifies
itself; the command may be interpreted as saying "Hello, I am
<domain>".

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Example of Connection Opening

R: 220 BBN-UNIX.ARPA Simple Mail Transfer Service Ready
S: HELO USC-ISIF.ARPA
R: 250 BBN-UNIX.ARPA

Example 5

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