Is a POP3/IMAP combo possible?

[#1]

It's really useful to have your latest emails (sent and received) co-ordinated on multiple devices (IMAP) but I don't want old messages stored on the server in the cloud (and I find IMAP can work badly if the message store gets really big).  So I would like to archive my old messages to one of my machines.  This is something POP3 does well for your Inbox.  I can set it to download messages and delete from the server all that are older than a specified number of days.  But this does not work at all for Sent messages.
Does anyone know a strategy to achieve what I want with the minimum of manual intervention? 

[#2]

One thought, I have a filter/process set up so that when I enter the "inbox" any messages older than 5 days and with "read" without "unread" status are copied moved to another folder. Perhaps two filters, one for sent and one for the inbox? BTW, I use claws-mail, so you're now on your own now
Phil

[#3]

Pardon my ignorance of IMAP but is moving something out of the Inbox to a local folder sufficient to remove it from the server Inbox and all other local inboxes?  I auto-archive my old messages (Outlook) so presumably that might do the trick.

[#4]

You are right - Thunderbird has an "age greater than" option when creating filters.

[#5]

Quote from: ReedRichards

Pardon my ignorance of IMAP but is moving something out of the Inbox to a local folder sufficient to remove it from the server Inbox and all other local inboxes?

Only if the other clients synchronize with the server. The imap protocol is a synchronization and download protocol. The local client should obtain a folder list and then a list of messages in each folder and replicate that locally for display purposes. IF the auto sync is disabled then nothing will change on the other devices but in reality most devices using IMAP do auto sync.
So yes is the short answer you can move it out of the inbox to another folder.
That said you mentioned 'local' folder - by this I'm assuming you mean another folder on the server. If you mean actually dragging your emails out of outlook into a windows folder and then deleting from the IMAP server, that deletion should be replicated across other devices BUT it's possible some of them won't accept deletions when they sync.
Me personally, I would do as PeeGee says.. I would have an archive folder that my rules / filters move things to after X days and that way at least your normal folders should remain useable. Downloading directly to your HDD could be a long boring manual job unless you have a client that will download, save and ignore further syncs.

[#6]

Thunderbird will quite happily move mail from an IMAP account to local folders which effectively is a delete from IMAP.

[#7]

Quote from: ReedRichards

....  I would like to archive my old messages to one of my machines.  This is something POP3 does well for your Inbox.

Quote from: 7up

.....  That said you mentioned 'local' folder - by this I'm assuming you mean another folder on the server. If you mean actually dragging your emails out of outlook into a windows folder and then deleting from the IMAP server, that deletion should be replicated across other devices BUT it's possible some of them won't accept deletions when they sync.

Though I mainly use dovecot running locally for incoming mail (originally to reduce the downloads during "metered" time and downloading e-mails with attached photos etc. after midnight ), I also use IMAP access to a couple of external servers and filtered "moves" into both IMAP sub-folders and to "local" (on the reader system) folders have the same results on various devices (including mobiles) of deleting the local reference to the server deletions with all servers.
Phil