Hi,
I strongly dislike Thunderbird, and sylpeed kept on locking up for me, so I moved to trying kmail (which is what I use on all my "real" computers)
I too could receive but not send. The problem was the missing library:
/usr/lib/kde3/kio_smtp.so
There is a missing dependency on this for the kdepim package. This library comes from
kdebase-3.5.8-5.fc8
I just yum installed kdebase, BUT that is pretty massive, so you could try putting just that library in?
I also found the authentication mechanisms were not installed, for things other than plan text, eg:
cyrus-sasl-ldap-2.1.22-7
cyrus-sasl-lib-2.1.22-7
cyrus-sasl-md5-2.1.22-7
cyrus-sasl-ntlm-2.1.22-7
cyrus-sasl-2.1.22-7
cyrus-sasl-plain-2.1.22-7
cyrus-sasl-gssapi-2.1.22-7
Now I am very happily using kmail!
Cheers,
Tim