In Snitz 3.0.00 the email option was available. Perhaps you could dig it out of the code. Here is a snippet of lines 534 - 552 from post.asp:
<% if lcase(strEmail) = "1" then %>
<% if Request.QueryString("method") = "Topic" or _
Request.QueryString("method") = "EditTopic" then %>
<font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>">
<input name="rmail" type="checkbox" value="1" <%=Chked(boolTopic)%>>Check here to be notified by email whenever someone replies to your topic.<br>
</font>
<% else %>
<%
if Request.QueryString("method") = "Reply" or _
Request.QueryString("method") = "Edit" or _
Request.QueryString("method") = "ReplyQuote" or _
Request.QueryString("method") = "TopicQuote" then
%>
<font face="<% =strDefaultFontFace %>" size="<% =strDefaultFontSize %>">
<input name="rmail" type="checkbox" value="1" <%=Chked(boolReply)%>>Check here to be notified by email whenever anyone replies to this topic.<br>
</font>
<% end if %>
<% end if %>