Add To Filter
In the PostBox application I can establish a filter for a sender's email address and attach it to a folder. Some senders have several people who may send me an email (think Udemy, for example). I would lilke all the emails from the sender to go to the same email and PostBox allows me to click and add an email address to an existing filter. Thunderbird won't allow this. If I try to set the filter for a new email from a sender (again, think Udemy), I'll get a notification that the filter has already been used.
A government office may also have several senders for a given department, for example.
Thunderbird needs an Add To Filter function.
Opaite Mbohovái (1)
Possible alternative: instead of making a filter that has multiple From entries with each one a different address, consider storing those addresses in a separate address book, AB, and then setting the From rule to 'is in my address book' and pointing to AB. Then, to add a new sender to the filter, click the sender in the message header, twice, to add the sender to AB.