Is this special case necessary?  I'm not sure I understand the error condition:
for example, if chunk is 2 and emails is 6:
```
In [1]: l = [0, 1, 2, 3, 4, 5]

In [2]: l[0:2]
Out[2]: [0, 1]

In [3]: l[2:4]
Out[3]: [2, 3]

In [4]: l[4:6]
Out[4]: [4, 5]
```