to be able to insert an additional subject from the recipient.

[jambolo]

In Thunderbird, the idea would be :
the quick search is often used to search for a mail on a particular subject, only it sometimes happens that the sender of the mail does not put an appropriate subject for the mail or it is a generic subject, which does not help if one has to do a quick search to find the mail.
So if the receiver of the e-mail could add a description or a secondary subject that fits in the quick search, it might help.
It could be especially helpful in a business context, for example if the sender communicates a price of an article that is not put in the subject line but in the body of the letter, then being able to add an additional subject line to properly catalogue the mail becomes much easier to search

Thank you. best regards.

[Jon]

Thanks for submitting an idea to the Mozilla Connect community! Your idea is now open to votes (aka kudos) and comments.

[Agentvirtuel]

Hello

Upstream of quick search

https://quickfilters.quickfolders.org/filtaquilla.html
Eventually ? if you'd like to test FiltaQuilla
https://addons.thunderbird.net/thunderbird/addon/filtaquilla

Installing an Add-on in Thunderbird
https://support.mozilla.org/en-US/kb/installing-addon-thunderbird
Enter the add-on's name FiltaQuilla or enough of it to limit the search results returned to a manageable number and press Enter or click the magnifying glass icon.