This should be an easy question for somebody.

One of my users copied a column of email addresses out of Excel and pasted
it into the BCC field of a new email. As the addresses began to list in the
field, some of them would appear grayed out and would cause a "ding" sound
to be emitted.

It appears that most of the emails were delivered (two were bad addresses)
regardless of wheteher they were gray or black, but any idea why these were

Can't seem to find the answer and it's bugging me.

Thanks in advance