You have an email address on a Raiser's Edge record that is marked as Inactive. When viewing a Constituent list in NetCommunity under Email>List, you notice this constituent shows in the results, even though their email address is marked as Inactive.
Records, which have email addresses marked as inactive, will show within constituent lists under Email>Lists in NetCommunity. However, NetCommunity will not actually send a message to them. Their email address will be excluded from the Final message.