@milkdesk
Let`s get through it one by one.
- You start with an array of Excel Rows
(as it is an array, referencing it would results in an apply to each ) - then select one property of this array to have distinct values on the e-mail addresses within the compose action with the union formula
(still an array, but only unique values, need this to send only one e-mail for all my associated rows) - Afterwards you loop over all previously gathered unique e-mail addresses
At this point you have one array as result of the filter array action (even though potentially your Excel file contains only one row for a certain e-mail address.
The other array is the unfiltered result of the List Rows present in a table action from the very beginning
Regardless which one you would select, the logic always presumes multiple potential items, thus adding an apply to each.
In case I would now want to have another property within my e-mail, the desired information is within the output of the Filter array within the Apply to each step already.
For me it`s the column ReminderDate, for you the CustomerName.
It might be that all filtered results show the same value for the column, but it couldn`t as well.

You could now do it exactly the same way as already done with the e-mail addresses.
Select the CustomerName from the output of the Filter array

Get unique values with union().
If you put it in another compose first and add its result to the e-mail or if you define it directly within the body of the mail is up to you. In case you want to review the Flow at a later point in time, it could be beneficial to have it broken down in more pieces.
Overview of the apply to each

Results of the two runs (as I have only two unique e-mail addresses in my table
1

2

I hope this helps you a bit further.