I haven't used Seamonkey in close to 15 years, but how does advanced search in the mail & news part of it in that differ from Thunderbird? I can right-click on one of the folders in my email account in Thunderbird and get a modal window where I can add or remove criteria to search for things based on header contents, attachment presence, junk status, etc.
It's similar to what I remember Seamonkey (and and the Mozilla application suite that preceded it) having.
Or are you comparing the quick filter feature in Thunderbird with advanced search in Seamonkey?
I think this could be it. Perhaps I did not explore Thunderbird enough to find the exact match feature. I was surprised because Thuderbird and Seamonkey should be from the same code base, so they should behave similar.
Anyway, thanks for your reply. I might try Thunderbird again after some time. I am very satisfied with Seamonkey, but am afraid that they might scrap the project at any time.
Especially during this Covid era, when the mail volume seems to have multiplied by a factor of 3 for me, search is really important. I don't want fuzzy search, but rather exact search. Strangely enough, the mail client that seems to get it right is also the one that is clunkiest to look at.