The FiltaQuilla add-on will let you set up a filter that will do this automatically.

I have done multiple searches for anything resembling "FiltaQuilla" but found nothing. I've also searched for anything to do with attachments, and still found nothing like "FiltaQuilla". Can you please provide more information so I can locate the Add-On and give it a try?

Top of this page click Mozilla, then Thunderbird, Addons. Search for the address n and you find this. https://addons.mozilla.org/en-US/thunderbird/addon/filtaquilla/?src=ss

Thanks AirMail for helping me locate the add-on. I don't know why it wouldn't show up before. However, I installed FiltaQuilla and told it to detach my attachments. I don't remember getting any option to set the directory into which I want the attachments placed. The few attachments which have come in recently (this isn't the busy part of the month) have not been detached but I do get a "Save" box in the bottom right, and if I click on that, or select 'detach' from the menu with it, the attachments are put in a directory which I still have to choose. Either FiltaQuilla doesn't do what I need - saving the attachments without me doing anything - or I'm missing something in the setup. I've just reset the option to detach but I got no option to set where the attachments are to go.

Whilst I do not use this addon, here is some info; http://mesquilla.com/extensions/filtaquilla/

Thanks Toad Hall. I omitted to add that I had already gone through the filtaquilla page you quoted. It says, about saving or detaching attachments, that "This action saves[detaches] all email attachments for the matched email (if it has any) to the selected folder. However, though Thunderbird|Tools|Options|Attachments specifies a directory on my C: drive nothing gets saved there, and nothing gets detached.

You have to specify the folder in the filter creation window, as in the picture (click the 'select a file' folder icon). First, make sure Save or Detach Attachments are enabled in the FiltaQuilla Options.