[Exim] SMTP Timeout?

I've 'inherited' an email server running Exim v3.3 on Solaris v2.8,
and whilst running EXIMON I've noticed the queue graphic stats going
from a steady flatline to a /|/|/| sawtooth pattern, and some messages
stating:
"T=internal_smtp defer (-44): retry time not reached for any host"
Could anyone shed any light as to what this means and how to resolve it?

Thanks.

Regards,

    Ken Jackson,
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