I am aware that has been the issue right up till now having no way to link back to a customer by manager and thats fully understandable based on what you have said.
I put to you a suggestion or idea and ask @lubos and anyone else who could suggest something better than what i say now.
would it be possible to have a check box or field on the bank transaction entry screen next to the Payer name field to place the customer name there , so it will appear twice or just have a tick box to say customer so manager can know this entry is related to an actual customer name and use that as the default for email address when email is requested by user.
this request seems to only be relevant when emailing a receipt to a customer after payment received so I don’t think we would need anything more than a simple checkbox , if a customer you tick the box that says customer and if not leave blank.
I can’t see a reason for Supplier box or dropdown list to be added but others may see a reason?.
Thanks for your update and I hope this suggestion may solve this problem for all users.