WLM appears to have sent out BCC addresses

Hello,

Yesterday I sent an email to about 100 addressees: 10 in the CC box and 90 in the BCC box (I used a dummy "group" address in the To box).

So far I have only had a few responses - but one from a CC person displays (between her reply and my original message below it) the last 70 of the 90 BCC addresses!  (But no others.)

How can this have happened?  How many other recipients can see the list?  Should I send out an enquiry & apology?  How to prevent it happening again?

Curiously, when I open my sent message, I can only see the first 20 of the 90 BCC addresses listed, instead of all these as I would expect.

Is this a clue: when I look in Properties, all the addressees are listed - but BCC No 20 is the only one to be followed by a semi-colon instead of a comma.

I should mention that I copied the addresses in from an Excel database column (in which every address is already terminated by a semi-colon - otherwise, I discovered, WLM can't cope with them at all!).

Thank you for any assistance.