I've never used NAnt but can offer two other solutions...
1) Create an email mailing list and add all the people that require it to the list.
Then create a teamcity user for with its email to to the mailing list and setup the required notifications to that user.
Restrictions to this is you have to create a user per mailing list which can eat up the licenses.
2) You can use the TeamCity REST API to get that information from the running build. Use %teamcity.build.id%
which will return the build id and perform the following lookup:
/httpAuth/app/rest/changes?build=id:%teamcity.build.id%
Which will return all the changes for the build which will like:
<changes count="3">
<change href="/httpAuth/app/rest/changes/id:217404" id="217404" version="b6b97a0d7789d97df6df908ab582ebb723235f43" webLink="http://teamcity.my-domain.com/viewModification.html?modId=217404&personal=false"/>
<change href="/httpAuth/app/rest/changes/id:217403" id="217403" version="064ecef5552ec2fb7875d7c26fe54cdf94b67bec" webLink="http://teamcity.my-domain.com/viewModification.html?modId=217403&personal=false"/>
<change href="/httpAuth/app/rest/changes/id:217402" id="217402" version="9bc3a34c952059bbfc7bebeb79ba5a3c894ef555" webLink="http://teamcity.my-domain.com/viewModification.html?modId=217402&personal=false"/>
</changes>
Then loop through the href
url results for each of the <change>
elements. Which return something like:
<change date="20130918T133404-0600" username="welsh" href="/httpAuth/app/rest/changes/id:217397" id="217397" version="51e925e354a83deccde881b30a76974b2ff745f4" webLink="http://teamcity.my-domain.com/viewModification.html?modId=217397&personal=false">
<comment>
My comments are here
</comment>
<files>
<file before-revision="90acd4da1972814094c22e3020c5073521a7b640@141323126c0" after-revision="51e925e354a83deccde881b30a76974b2ff745f4@1413290abe0" file="grails-app/views/layouts/global.gsp" relative-file="grails-app/views/layouts/global.gsp"/>
</files>
<user href="/httpAuth/app/rest/users/id:1" id="1" name="Welsh" username="welsh"/>
</change>
And use that to build your email to who you email to whoever which is more work to create initially but more freedom on who you email without eating up licenses.