Yes -- make the recipients accept it faster.
Seriously, by default qmail makes a maximum of 20 concurrent outgoing connections. To temporarily increase this, put a larger number in
/var/qmail/control/concurrencyremote
Note that your change will be clobbered next time the template for that
file is expanded, so if you need the value to be permanent, make a
custom template for that file.
Cheers,
--Rich