This looks like you're defining the filter on a Sent folder instead of an Inbox. Open Tools/Message Filters, select the filter, then check the account at the top and the 'Run selected filter(s) on' folder.

Thanks to S F Howes for taking the time to respond. Thanks for suggestion but I am receiving to an inbox. I re-tried my filters being careful about following the suggestion but get exactly the same result. Further suggestions are welcomed but I can live with using "To..." rather than "Recipient..." if necessary. It just seemed a bit odd that one would work and the other not.

Filters are limited to the header fields and their contents. (with the exception of Body) Incoming mail has a To: and a From: header field, not a recipient.

When I check the registered email headers https://www.iana.org/assignments/message-headers/message-headers.xhtml I do not see recipient listed. Did you add it yourself through customize?

Hi Matt, Thank you for responding to my enquiry. If one goes into Thunderbird email client and right-clicks on any heading on the Folder pane a series of options for column headers in this pane is presented. Included in this list of options is "Recipient" which I use. It is not a customised setting. If one goes into Thunderbird, Tools, Message Filters, and sets up a new filter, in the Match pane if one clicks on the box which is pre-set to "Subject" one gets a list of the same options as show in the Folder pane, and one can select any of the options. There is also an option "Customise..." but this is not used in the problem case. I would have thought that these options would have been local to the software supplier (Mozilla) and not subject to a generalised control (except perhaps for a number of accepted global options) and as such I would expect them to all work in a similar manner.

I am no closer to arriving at a solution, but as I mentioned in my earlier posts this is not really a great problem as I currently have a workable alternative which I can use.

In the attached picture you can see the available criteria for filters in TB 60.5.3 (plus a few custom ones). There is no Recipient entry, as this is provided by the To header. Are you using a current version of TB? Recipient is certainly an available column in the Threads Pane, but as noted above, it's not a valid header, and the columns and headers are separate things.

It looks to me that you're using the Quick Filter Bar, which has Sender, Recipients, Subject and Body as criteria. Obviously, Sender is more relevant to the Inbox than Recipients.

SeatAdvisor said

Hi Matt, Thank you for responding to my enquiry. If one goes into Thunderbird email client and right-clicks on any heading on the Folder pane a series of options for column headers in this pane is presented. Included in this list of options is "Recipient" which I use.

There is also one for correspondent. it is not in the email header either. There is a lot of difference in the pretty way things are presented in a user interface and the realities of an email header. Recipeint is not in the header, so it is not suitable for filters.

It is not a customised setting.

That is taken from a new Thunderbird profile and shows the available fields for filters. Anything else is a customization. As you can see. Recipient is not there.

If one goes into Thunderbird, Tools, Message Filters, and sets up a new filter, in the Match pane if one clicks on the box which is pre-set to "Subject" one gets a list of the same options as show in the Folder pane, and one can select any of the options.

Nope, not the same. Similar, but not the same. Recipient for instance is used to replace the To field in the sent folder headings because someone at some time thought it sounded better. Probably someone at Netscape corporation in the last millennium. I see no reason why it would have ever been changed as it is not ambiguous and also make it clear which folder you are in. (except where you have chosen to use it elsewhere.)

There is also an option "Customise..." but this is not used in the problem case.

I have no idea how it got there then. I just created that profile so I could see the defaults because mine is heavily customized.

I would have thought that these options would have been local to the software supplier (Mozilla) and not subject to a generalised control (except perhaps for a number of accepted global options) and as such I would expect them to all work in a similar manner.

Filters use the unvarnished message as it arrives. Press Ctrl+U to see what the filter sees. (message source)

What appears in the message source and particularly the message header is regulated by standards. That is why you can send mail in Thunderbird to folks that don't use Thunderbird. The message format/ transmission format is regulated under a standard, a whole host of them really. but the headers of emails are regulated as I said, Although the use of X- headers is not regulated and a lot of use is made of them but larger mail providers like Yahoo, nti virus programs and even by Thunderbird itself. For example Thunderbird:

X-Account-Key: 
X-UIDL: 
X-Mozilla-Status: 
X-Mozilla-Status2: 
X-Mozilla-Keys:    

Yahoo:

X-Yahoo-Profile:
X-Yahoo-Newman-Property:

Anti virus (from a single mail in my inbox)

X-Antivirus: AVG (VPS 190215-10, 02/15/2019), Outbound message
X-Antivirus-Status: Clean

Looking at the message source should leave you under no illusions as to what fields you can use and which you can add through customization.

I am no closer to arriving at a solution, but as I mentioned in my earlier posts this is not really a great problem as I currently have a workable alternative which I can use.

You will not get to a solution. I hope you now understand why. If not, I can try again to explain it. But the short is your searching on a non existent value in the data to be filtered (the email source) instead relying on a user interface label that has no validity outside the user interface.

Hi Matt,

Thank you for taking the time to run through the email filter structure. What you say is reasonable though sensible from a user's perspective since one presumes that if an option is offered then it will work. Not many users are conversant with the inherent structure behind an application and in many cases software designers actively go out of their way to obfuscate the way in which their products work. I can live with the result and now I am aware of why it occurs - doesn't mean I applaud Mozilla's approach to offering facilities to users who may not have the understanding that you have but hey - you don't rent software and expect it to be reasonable.

Regards