Recently I went through the process of getting my new key (C99E03CC is dead, long live 43C30A7D!) signed to replace the old one in the Debian keyring. Some people used caff to send out their signatures and in 3 different cases I did not receive the signature for my uid, leaving me somewhat dumbfounded as signatures for other uids went through just fine, as did various test emails to my address. After pestering people on IRC and discussing the issue with one of the signers, we concluded that Debian's mail servers are configured to reject any mail with invalid envelope-From header - and chances that caff-sent email is going to have an invalid one are pretty high. As far as I can tell, a valid configuration is such that

echo ${USER}@$(cat /etc/mailname)

returns a valid email address. So, if you are a caff user, please make sure that your system is configured correctly before sending out signatures with it, namely that the emails sent using something like

echo 'test' | mail ${YOU}

are getting through successfully.