Is there any way to eliminate complete conversations within the Inbox or within the Archive?
I miss a Recycling Bin. This would help not to fatten the forums. Have a little maintenance by the user with their private conversations.
Is there any way to erase them and not see them anymore?
ATM moving from inbox to archive is the only option for users. I believe that even if you had a trashcan icon available Raul your message is not deleted/erased, it would only get a hidden flag in the database.
Since we have new forums, this could be improved. Certainly, it is limited in this way. I think the right thing is for the user to have some control over their inbox, because it’s theirs. I should be able to manage it.
If it is not possible to delete, unless there is a third folder called trash or something like that. Yes, we can use “archive” to throw the unwanted messages, but it seems that this folder is for something else.
A “delete” option would be great. We would eliminate a lot of garbage among everyone, and the forum’s database would not get so fat.
Raul you could also take up the matter on the discourse forum. Example thread https://meta.discourse.org/t/how-to-delete-private-messages/51202 
As for ‘database getting fat’, I agree, I’m not much for large bloated databases myself. Though when you say ‘database’, I live in 1985-86 with Mini Office and a C64/Amstrad CPC or maybe early 1990’s dBase III Plus from Ashton-Tate software Raul. Tends not to be SQLite or PostgreSQL or MySQL…
In this link a user asks What would happen if a user deletes a speech from his inbox? Remember that it IS YOUR ENTRY TRAY.
Well, the other participants of the speech, if they participate again, a signal would appear indicating that said user has abandoned said speech. And that’s it. There is no problem in that. Another thing is that the forums are prepared to work like this.
I do not know what need to keep certain speeches when the user does not want to see them in his inbox or in his file.
It’s not that I care about the matter. But yes to keep the discourses in order.