Please check /var/qmail/control for the following 2 cert files:
dh512.pem
dh1024.pem
If you don’t see them or with another naming (dhparam512/1024),
rename them accordingly.
#cd /var/qmail/control
#cp dhparam1024.pem dhparam1024.pem.bak
#cp dhparam512.pem dhparam512.pem.bak
#mv dhparam1024.pem dh1024.pem
#mv dhparam512.pem dh512.pem
#service xinetd restart
#service qmail restart