I was hoping that I could make a manual list without error but it did not work, here is the procedure (my own) I followed:
Despite trying to be meticulous, I have errors in the result.
Can someone suggest a better way for an email service provider (mailbox.org) that seems to have succeeded at restricting to the maximum what their customers can do?

Paying more than the base plan does not seem to provide any advantage.

Thank you for your help.

Without knowing anything about the provider, and without any description at all of the the errors in your result set, it is impossible to offer any specific advice.

It appears to me that you are simply printing what you have selected to a file, so if there are errors (or omissions maybe?) then they may be in what you have selected. If the selection is controlled by javascript from the provider then they may limit your selection.

In any event, it seems to me that this is not a programming problem, rather you should probably contact your provider for help with their application.

Good luck!

Expecting a usable answer from such services is expecting too much, instead and although I did not explain it well I was anticipating that numerous service providers are using very much the same procedures or similar ones and that there could be a "generic" approach that could be used in most cases.

Not allowing their customers to take a screenshot for example is not typical of some clients of email services or themselves, it is widespread as when one does it, others then only copy even if they devise their own procedure which uses the same code.

My email service provider for example provided a backup of a couple of emails I accidentally deleted, when their "answer" about it is good publicity, the back up, for which no link is provided, is nowhere to be found.

But it's OK if no one has an answer, it's a risk one takes when asking a question.

Can't you just use IMAP and a mail client?