On the second day, the executive receives 16/2 = <<16/2=8>>8 new emails.
On the third day, he receives 8/2 = <<8/2=4>>4 new emails.
On the fourth day, he receives 4/2 = <<4/2=2>>2 new emails.
Therefore, during the entire trip he will have received 16 + 8 + 4 + 2 = <<16+8+4+2=30>>30 new emails.
#### 30