April has thirty days, so half will be 30 / 2 = <<30/2=15>>15.
For the first 15 days, he received 20 * 15 = <<20*15=300>>300 emails.
For the remaining 15 days, the number of emails increased to 20 + 5 = 25 emails.
The total number of emails for the remaining days of the month is 25 * 15 = <<25*15=375>>375 emails.
The total number of emails for April is 375 + 300 = <<375+300=675>>675 emails.
#### 675