emails is an array (or specifically an ArrayList) of objects of the class Email. The loop is a 'for-each' loop which uses the syntax:

for (datatype variableName : collection) { 
    ...
}

This means: for each item in the collection/array, store the item of type datatype in the variable called variableName. This variable can be used within the body of the for-each loop, which is executed for each item in the array.

For example:

int[] arrayOfAges = {18, 22, 21, 19, 27};

for (int age : arrayOfAges) {
    System.out.println(age)
}

Will produce the following output:

18
22
21
19
27

So the for (Email email : emails) means get each Email object in the ArrayList emails and store a reference to that object in the variable email.