Hello Thomas,

The emailing system is quite confusing for most people since it's not perfectly intuitive (strictly personal opinion)

When you send a business document by  "Send Email" button you are not infact sending to the address you have on top but more to the followers of the document.I remember having this issue in the past where I would add a new address on top and I would get emails in 3 inboxes (while debugging I had access to all those inboxes).I soon found out that the system pretty much ignores what you put in the sender and just sends to the followers of their document, of course, it also takes a look on their options (opt-out, receive messages etc)

In order to have your system working you should:

1.Have a outgoing mail server that's configured working & tested

2.Have in the document that you are trying to send the the right followers (Customer is automatcally added when saving the quotation)

3.Check the options on the followers and make sure they are not opting out of the email messages which blocks your actual docs

4.Keep and eye on the log and check the email status in Settings->Technical->Email->Emails

It has been quite a while since I've worked with the emailing system so I hope I have not provided any imcomplete/false information

Hope this helps