You archive a message because you are sure you could need it in the future. But for how long? It depends on the content of the e-mail. The archiving function handles all messages the same way. Messages are grouped by date. By the date they were posted, but not by how long we want to keep them.
The solution would be that when archiving, the MailSpring client would ask you how long you want to keep the email.
This sounds very like the “Snooze” feature that’s available in the Pro version of Mailspring…
“snooze” brings back the message to the inbox. This function would move it to the trash.
So do you want a feature to auto-delete messages in the Archive after a period of time? But configurable per message?
Perhaps a workaround might be something like (given that this would be manual anyway): create a series of folders with auto-delete times set up for (say) 7 days, 30 days, 180 days, and then move the messages into one of these folders instead of the default Archive?