Clarification on purpose of subordinate keys

[John Harrold]

Hello,

I've been signing my emails with my gpg key (F65A739E) at least that is what
mutt says.  However,  when it's sent it appears to be signed with a sub key
(B23241CB). Can someone explain the purpose of subordinate keys and what I'm
doing wrong?

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pub   1024D/F65A739E 2002-10-02
uid                  "John M. Harrold" <jmh at member.fsf.org>
uid                  John Mark Harrold <jmh17 at pitt.edu>
uid                  [jpeg image of size 5337]
sub   1024D/B23241CB 2003-10-01
sub   1024R/C7658196 2003-10-02

-- 
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                            | /"\                         
 john harrold               | \ / ASCII ribbon campaign   
 jmh at member.fsf.org      |  X  against HTML mail       
 the most useful idiot      | / \                         
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 What difference does it make to the dead, the orphans, 
 and the homeless, whether the mad destruction is brought 
 under the name of totalitarianism or the holy name of 
 liberty and democracy?
 --Gandhi
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  gpg --keyserver pgp.mit.edu --recv-key F65A739E
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