I'm not aware of any such command 'Just delete attachments from selected messages', so I would suggest it's provided by an add-on you've installed or possibly an antivirus program. In the absence of a filter, you cannot delete attachments from multiple messages in TB.

It's in the Message menu under the Extract options. I think sfhowes is right about the add-on, because I have attachmentextractor-1.3.5.1-tb.xpi among the installation files, so I'll take this away to that add-on group, thanks. Regarding Thunderbird, I particularly value the facility to post-delete attachments whilst leaving a corresponding report in the mail. Pity it can't do the same to inline images, for which I have to resort to Outlook.

given removing attachments fundamentally alters the content of the message, I can see Microsoft's exchange based mails servers changing the date on the email for IMAP folders.

As for outlook allowing post delivery editing of the message to remove unwanted bits. Just what sort of an audit trail is left in Outlook for when the legal letters starts flying about who send what to whom. It might be convenient to edit the mail someone else sends you. But once you have done that it has zero legal validity as something yo received. About as much weight a a photocopy. Not the original and not admissible usually.

There's no conspiracy here. Given limited server space, you can keep a much longer history of mails if you delete attachments, and you certainly don't want those mails re-dated. Generally you will always have a copy of attachments you sent, yet TB doesn't offer deleting them by default. Received message attachments may need archiving before deletion. I'm not a lawyer.

You may find the ATTACH EXTRA TOOLS add-on useful, as it has the option to delete attachments from sent messages, although it is done on a message-by-message basis.

Otherwise, the FiltaQuilla add-on gives the option to detach or delete attachments from sent or received mail via a message filter.

Thanks for the suggestions. I installed Attach Extra Tools but found that it generated multiple sent mails, some still containing the attachments, so worse than useless, unfortunately. My appetite for add-ons is now very low.