How to exclude column data

I don't understand your "output" column - should the results not be 2, 3 & 4 rather than 7, 8 & 10 ???

If you want the mailto listing in a ; delimited string for copy/paste I would suggest using your sample file:

C1: [blank]
C2: =C1&REPT(";"&$A2,ISNA(MATCH($A2,$B$2:$B$7,0)))
copied down to C7

The final mail listing is then simply the contents of C7 which you should find you can copy & paste into your mail item.

Modify ranges (& recipient delimiter) per your own requirements.