Exploring ways of removing messages from mailboxes for my dad who uses Gmail and Thunderbird I thought I’d also try it on my own Runbox.

I created a folder under LocalFolders, selected the messages using the filter and then dragged them to the newly created folder. In Thunderbird they no longer show up in the Inbox but in webmail they appear with the subject displayed with strikethrough.

Does this mean they are marked for deletion?

Hello and welcome to the forum.

Yes, that’s correct. The Runbox 6 webmail actually shows you the correct status of messages rather than just showing them as deleted. As you’ve discovered sometimes a message is marked for deletion but not yet actually purged from the mailbox. This is a little known IMAP feature as you can then mark the messages as not to be deleted again if you wish.

We decide to show this as a strikethrough in the web interface, but actually it causes more confusion than it is helpful so like other web apps we dropped this in the new Runbox 7 and messages are just shown as deleted.

You can tell Thunderbird to purge messages marked for deletion or often they are deleted when Thunderbird is closed. I hope that helps.