Better way to manage email list

We have about 20k on a email list we have. We need to separate this list in increments of 300 in seperate files, so it can be .txt or csv. Does anyone know what the fastest way of possibly doing this would be?

 

write a small php script which does the separation for you.

any particular reason for 300 in one file?

 

Yup. I thought of that also. A php script would be quicker.