Archiving sent webmail

[#1]

I have an old email address going back to Madasafish and Freenetname which I understand has a hard limit of 100Mb.

I seldom use webmail now, since I converted from POP3 when I discovered IMAP could sync between my Mac, iPad and iPhone. However sent messages using webmail are not synced.
I've been getting quota warnings occasionally and bounced messages. I have 275 sent messages on webmail which I would rather keep than delete, so I would like to save them to my Mac if possible. I have tried the 'download' option in the settings, using a batch of mails, but that only delivers an empty .zip file to my desktop. I wonder if there is a solution to this?

[#2]

The "right" solution to this space is NOT POP3 as many might suggest.

POP3 downloads only the inbox, because in a POP3 set-up there is no concept of the other folders being held on the server.

Personally, I would revert to IMAP, create within the IMAP client a local folder for your historic sent items, then drag and drop those items from the server's sent items folder to your local folder.  Then remember to back up your computer regularly!!

Email housekeeping is something we all ought to do better, rather than leaving it to technology to muddle through unaided.  POP3 is not the panacea many suggest that it is, invariably it creates unhelpful complications, especially where the mailbox is accessed on more than one device.  Proper self-managed housekeeping (culling and archiving) using the tools of the IMAP client to store content locally ... along with a robust back up practice is highly desirable.

[#3 · Accepted solution]

Thanks but I found a solution last night.
I'm already using IMAP but it's not clear from your message if you knew that.

There are 2 folders on plusnet webmail, one called 'sent' and the other 'sent messages'. The first folder contained all the old messages from when I had a POP3 account, and is static. The second folder had recent messages. I just had to shift the old messages to the other folder which is linked to the IMAP account and so is dynamic.
I already have a local folder on the desktop as you described so I just moved them there afterwards.

[#4]

There might be several sent items folders if you have used multiple devices connected to the mailbox. Some email clients play nicely and look for an existing sent / trash / drafts folder and use it. Some are wilful and determine for themselves what to use. Therefore you can end up with multiple folders for the same purposes.

Win10 mail is notoriously bad for this.