Steps to reproduce:
This issue has been an issue for around a year, I've gotten around to looking into it recently. Outlook (office 365) now is supporting larger files in email protocols, we're seeing 21-30MB files, this is where thunderbird is having issues.
It is very easy to reproduce this, and it works on every OS, your mail server may not support the files that are this big though.
email yourself a file that is larger than 21MB, I recommend just .tar ing several files together or something
(you will get a filelink msg that recommends using that, however the people whom we get the emails from are generally using outlook (office 365) and they do not get this message, obviously, so it is irrelevant here)
when you view the email, especially the source, you'll see that it's actually a good email and the base64 encoded file is there, and it works. You can easily copy paste the giant base64 message, save it into a file and run "base64 --decode filename > file.tar" and it'll work, the file works perfectly, this works with any file... thunderbird fails to save it though
save the file, it'll save as like 27bytes of data or so, and it won't open, obviously. I've tried every "attachments" addon, it seems they all use whatever thunderbird does internally because they fail as well, I figured at least one would do base64 decode on it's own..
We get a file (anyone on my 17 person team) and can't open it if it's too big
We should be able to save the file since the "view source" has the correct file, but base64 encoded.
I have tested this on:
blue mail (android)
outlook (desktop, android, and iOS)
gmail app (android)
all of them work, except thunderbird, with the same emails.