Can't delete emails in webmail; messages reappear in email client after deletion

[#1]

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@Tontoe wrote:

I've just deleted 4000+ messages in Mac Mail for the umpteenth time and - guess what? - they all just keep downloading to the inbox again.

This happens however I sort the messages in the email client.

I know Mac Mail ain't the best, but it works with my other five [non-plusnet] ISP email accounts.

I'm just wondering why Webmail would keep regurgitating deleted messages to my client inbox in this way? I thought the idea of IMAP was that once you deleted a message in your client, it was deleted on the server?

Using the sort options in the grid in webmail supposedly refreshes the page, but there are still no emails showing in the content window, and the info bar still shows 11,000+ emails [see screenshot]

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If you are trying to delete 4000 emails as a single transaction, you are inviting issues.  That is asking a lot of work of the server and most probably the IMAP CLIENT is timing out the server and trashing the transaction.

Yes IMAP does work as you suggest, but they need to sync the changes - the client gives the server an instruction and then waits for the server to complete that task.  You you instruct the server to ACTUALLY delete 4k items (MOVE them to the deleted items folder) that will take time, possibly more time that the client cares to be patient about.  Does that Mac offer server timeout settings?

Whatever the delete key sequence is, try holding the shift key at the same time to see if that MARKS the items for deletion.

You can do that in webmail.  You can also alter the setting in webmail as described in post #3.  How many items per page have you set webmail to display?  The standard setting is 40.

The sort sequences is only an issue in webmail.  Looking at the screen shot, I suspect that you have this sorted on FROM ... which is not NONE ... and is at the heart of a known performance issue with Roundcube webmail.  I also observe that you have SELECTOR as one of the display columns - try dropping that column.

Look at the delete action configuration options described in post #3.

[#2]

First off, I know you're not a Plusnet staffer, @Townman and I appreciate your taking the time to try to help, honestly I do  

To respond to your points:

Over the last six months or so I have tried deleting anything from a single email to larger groups.

I only deleted the 4000+ emails as a kind of last-ditch experiment.

Whatever number of emails I delete in my client, from a single one to multiples, the result has always been, and still is, the same - the server regurgitates them and they appear in my client inbox again.

To reiterate, I have tried holding shift down at the same time as either hitting the delete icon, or pressing the Mac key combination [fn+backspace]

As I have already said, I have tried changing/reducing the number of emails visible in the data window in WebMail. Whatever number I pick, no emails show; the messages window remains blank. Therefore, I cannot shift/delete emails in Webmail, because there are none showing.

I did read and digest post 3, thanks.

My point is that the webmail interface is non-functional for me - I can't alter the columns or the sort order, or in fact do anything with messages, as there are none showing.

When I try to change the sort by clicking, the window starts refreshing [showing "loading"], and also showing "Mailbox is empty" in the info bar [see screenshot] and eventually comes back to a blank, with 11,000+ messages in the inbox. Interestingly, there are nowhere near that number of messages in my client inbox. I wonder whether the server is somehow regenerating/copying the messages it kicks back?

All options for the inbox in the l/h are greyed out when I move the cursor over it.

I have tried accessing webmail on other machines [PCs] and operating systems [Windows 10] with the same result.

I've also re-attached the screenshots of some of the IMAP error messages in case this helps.

Thanks again for taking the time to help.

[#3]

turns out Plusnet had archived all the emails without telling me.

slowly going through 12,000+ mails in cube mail now and deleting them in batches of 200.

BTW tech support person said Plusnet email would be stopped completely very shortly.

I have a Plusnet domain [which is why I have to use PN Webmail], so will be trying to transfer this out...

[#4]

There is nothing more than hearsay on the future of email services.  Such closure has been the subject of speculation for over two years.  Sadly much of what first line speculates about does not come to fruition.