OK. That makes sense.
In all faxing problems, there are three main sectors of concern:
1. the faxing machine, at this end.
2. the line between sending machine and receiving machine.
3. the faxing machine, at the other end.
In this case, I suspect that what you have is a problem with the machine at the other end, with one particular number perhaps.
The test fax went through without the usual pause-and-redial hitch, so basically that proves that your fax machine is without fault in the normal course of things.
If you can 'listen in' to what is going on with the pause-and-redial, to see if there's a voice message or the like, then you might get a good clue as to what is causing the problem, and where. I suggest doing that also.
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