[Exim] delaying large mail

Hi, friendly exim people!

I've got a rather strange query here and am hoping some guru out there
will be able to help.

Is there any way, using exim, to cause e-mail messages above a certain
size to be held in the queue (outbound) or "temporarily refused"
(inbound) until certain times of day? My situation is that I have a pretty
heavily utilised link to my upstream ISP from early morning until early
evening but utilisation drops off to a bare minimum later on. I would
like, if possible, to lessen the load imposed by e-mails with largish
attachments (those poxy images/mpegs/powerpoint thingies, for example) by
timeshifting their acceptance/sending to times where I have more available
bandwidth, freeing up bandwidth for the smaller stuff.

Any pointers, even ones telling me to wake up and smell the coffee
(strong and black), would be most welcome.

- Sean

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