Wikipedia has a checkmark for "Virtual Folders".
I put some comments on the bottom of the "Talk" pagehttps://en.wikipedia...son_of_email_clients
Virtual Folders Ritlabs- TheBat! is very strong. (I have dozens in my Bat.)
Thunderbird-Postbox (not on list) definitely, by saved search. Seamonkey probably, since, like Postbox, afaik it is a fork on a Thunderbird code base. See - https://www.lifewire...-thunderbird-1173118
Afaik, Eudora does not have virtual folders in any way, yet it is marked yes. I am a long-term Eudora user.
And I am a little skeptical about Mailbird, Em Client, and the Opera ("all folders are virtual") entries. Also Pegasus, Poco and Zimbra. Maybe so, but since Eudora was called yes, all should be checked. I will do what I can, only working with Windows clients.
And I recommend adding Pandora and Postbox to the list.
"Opera Mail is at the end-of-life stage of its product lifecycle; this means neither technical support nor product and security updates will be provided. The product is no longer available for download."
It actually does seem to have an interesting architecture.
Lifewire - 2019https://www.lifewire...7-free-email-1166878
"Pegasus Mail does not include virtual folders or labels that would learn by example. If you're accustomed to your email program realizing that you put all your emails from your spouse into a "family" folder, for example, and then shortcutting that move, you'll be disappointed in the inflexibility of Pegasus Mail to automate these tasks for you."
Poco (or its sucessor) seems unlikely.
"PocoMail for Windows is no longer available for sale."
Maybe Barca, but I have not seen the feature.
"The Zimbra Desktop is no longer supported. It will reach the end of Technical Guidance October 1, 2019."https://forums.zimbr...php?f=23&t=66134
WHAT ARE "SMART FOLDERS"?
Smart Folders are virtual folders that display all messages from a certain folder type (such as Inbox, Outbox, Sent, Unread, Flagged messages, Search Folders or Category folders) from all of your email accounts at once. They can be found in the left pane in the Mail tab, above the folders for your individual accounts. This feature allows you to check all emails without having to go through each separate account individually.
These folders can be enabled/disabled in Menu > Tools > Settings > General > General.
This does seem to be a virtual merged folder, a flat view, but not virtual folders in the sense of
"all emails in any box involving 'Johannine Comma' "
Mailbird has "Unified Inbox Plus" - doubt that they have any real virtual folders, by my understanding
Interesting article and discussionhttps://www.getmailb...ail-app-for-windows/
Bottom line so far -- just TheBat! for real, true, workable virtual folders in an active product.
A bit more.
Should check ChaosSoftware - Chaos Intellecthttps://www.chaossof...re.com/products.aspx
Compare to Essential PIM if use full Chaos stuff.
EasyMail for GMail - Gmail on your Desktop
(Some Notifiers do this too.)https://easymailforgmail.com/