freebody wrote:

How do I tell if a mail subfolder is local or on the provider's server
without going to the provider.

For
hotmail.com
gmail.com

You never bothered to mention which e-mail protocols you are using.
Hotmail/Outlook.com accounts can be accessed using POP, IMAP, or
Exchange. Gmail accounts can be access using POP or IMAP.

POP (Post Office Protocol) has no concept of a folder. There is just
the mailbox where all messages reside. There is no Drafts, Deleted,
Junk, or other folders in a mailbox because there are no folders in an
mailbox. Think of your filing cabinet but with no folders to separate
the documents, just all documents tossed into the drawer. Aebmail and
local clients will present the mailbox as a folder named Inbox but there
is no folder named Inbox in the mailbox itself. That's just how the
clients represent the mailbox. All other folders in a local POP client
are local; i.e., they are folders you created in the local message store
for that client and are not up in the server (since POP doesn't use
folders, just a mailbox). The Deleted, Junk, Sent folders are all
local-only with the client for a POP account. See:

https://en.wikipedia.org/wiki/Post_Office_Protocol

IMAP (Internet Message Access Protocol) does support folders. The
client will sync its local folders to the folders defined up on the
server. Often in a client you can decide which folders to sync but the
defaults are usually Inbox, Sent Items, and Drafts. Somewhere in
Thunderbird should be a sync folders option where you can select which
folders from the server will be created and synchronized in the client.
That way, you could, for example, create an Archive folder using the
webmail UI to your account and then add it to Thunderbird to keep a
locally synchronized copy of that folder, or create the folder in
Thunderbird and have it send a command to the server to add the new
folder. I don't use Thunderbird but somewhere within an account's
configuration should be synchronization options which can show you which
folders are being synchronized between client and server. Any other
folders you see in the folder tree would be local only.

IMAP does support the concept of folders for organizating or tagging the
e-mails. See:

https://en.wikipedia.org/wiki/Intern...ccess_Protocol

Despite Gmail claims to support POP and IMAP, Google started with a
webmail-only client and then did a frankenjob allowing POP and IMAP
access. Gmail uses tags, not folders, to organize messages. That means
a message could have multiple tags, but in IMAP a message is only in a
single folder. Gmail converts tags to folder names during IMAP access.
I have not tested into which folder a retrieved message gets stored if
it has multiple tags up on the server. Google decided some settings
would be configured only at the server which violates some functions in
the e-mail protocols. For example, no matter what you configure in your
client, having it delete a message after a retrieve (i.e., RETR followed
by DELE), the server will still keep the message unless you configure a
delete after retrieve. This can screw up an e-mail monitor which
retrieves a message using POP but then the user cannot retrieve it into
their regular e-mail client. Depends on how the server is configured,
not how the clients behave. Because of Google's variances away from the
standard e-mail protocols, access to Gmail should really be called gPOP
and gIMAP. Their close enough to POP and IMAP that typical scenarios
work but when you get fancy in your e-mail setup then you can run into
Google's screwups in trying to adapt their webmail service to POP and
IMAP.

I found this from Mozilla:

https://support.mozilla.org/en-US/kb...ynchronization

The client will poll the server for a list of folders that your account
up there has defined within it. A list of all folders returned by the
server are listed in the client (Thunderbird). You can then decide
which ones are synchronized (with a checkmark). Of the IMAP-capable
clients that I've used, they all had a means of selecting to which
folders they would sync up on the server (and any other folders
presented in the client are local-only folders defined only within that
client).