Button's should grey out, not disappear and thus move others

Checklist

• I have used the search function to see if someone else has already submitted the same feature request.
• I will describe the problem with as much detail as possible.
• This issue only contains a request for one single feature, not multiple (related) features.

App version

6.000

Problem you are trying to solve

I am using the unified inbox. One of my mailboxes (let's call it A) has an archives folder, others do not.
When I select a message in mailbox A, then on the top of the screen there is an archive button. When I select a message of any other mailbox, there is no archive button, causing the other buttons to move one position ot the right so that the (un)read button takes the place of the archive button.
The effect is that I'm used to the (un)read button being in the position of the archive button, so when I want to mark a mail from mailbox A as (un)read, I inadvertently tend to archive it.
Worse: by default, the buttons have no label, so I had no idea what the button even did, and it's not easy to google if you only have a pictogram to go by.

Suggested solution

I've been able to disable the archive button by setting the archives folder for mailbox A to none.

However, that's beside the point in my opinion. I think a good solution would be to grey out the archive button when it doesn't apply, rather than removing it, so that all buttons keep their place.

Screenshots / Drawings / Technical details

No response

Start by reproducing the unified inbox behavior in app version 6.000 with mailboxes that differ in archive-folder availability, focusing on the top action buttons. Done means the archive button remains in its position as a disabled or greyed-out control when archiving does not apply, while applicable messages retain the existing action.