I have an email account configured via IMAP in iOS Mail app, with
the Organize by Thread and Complete Threads toggles both turned
on in Mail settings.
Thanks to the latter, when I open an email from the Inbox or Archive
mailboxes, it is shown in the context of its thread, with the preceding
and following emails also being shown above and below the opened one.
However, when I open an email from the Sent mailbox, the thread view
does not activate, and only that singular email is displayed.
Is there a technical reason why Sent is being treated differently
from Inbox and Archive in regards to threading? Is it possible to
enable the thread view for emails opened from Sent, as well?
From my experience, this behavior persists both on iOS 13 and 14.
(Perhaps it dates all the way back to the introduction of the thread
view in Mail?) And, as far as I can tell, it does not seem to be
specific to the email provider.
Unlike iOS, in Mail.app on macOS, viewing an email from the Sent
mailbox does show the full thread it belongs to.
Best Answer
You are correct, the sent mailbox behaves differently than all the others in my testing with iCloud and O365 and Fastmail IMAP.
I wouldn’t presume to speak for Apple when they decided how to implement those switches, but their intent is very clear and easy to reproduce. Perhaps someone familiar with IMAP standards or other mail clients can see if this is typical for sent to be strictly ordered by time or that was just one team’s decision when they coded the app.
I see no configuration profile or setting to make sent work like inbox with respect to threaded treatment of mails.