Count number of distinct values in one column for each distinct value in another column

Question

In Pandas dataframe, I am trying to get a count of the unique values in a column for each distinct value in another column.

For instance if we have the dataframe below and we want to get the count of the unique values in starter_email column for each unique payment_email:

id       starter_email   payment_email       
22      1234@gmail.com    gzab@aol.com
22      1234@gmail.com    gzab@aol.com
30      2267@gmail.com    gzab@aol.com
12      3142@gmail.com    ccgc@aol.com

The ideal output would be:

   payment_email   unique_starter_email
   gzab@aol.com                       2
   ccgc@aol.com                       1

I know how to do the simple unique value count on 1 column only:

unique_starter_email=df['starter_email'].value_counts() 

But I wasn't sure how to get the count based on each unique value in another column. Any suggestion would be greatly appreciated!