Created attachment 122939 [details] htop prior to freeze and OOM (Note: perhaps this bug should be filed under akonadi and kmail too.) These are really two distinct bugs, both related to absurdly large attachments. 1. When attaching a really large attachment (try one of a few GB), Kontact crashes. This one is not so bad, you restart Kontact and it still works. 2. When attaching a large-but-not-large-enough-to-crash attachment (a 779,5 MiB file), it gets accepted but akonadi then completely chokes and uses 20GB+ RAM spread over its agents until kernel OOM killer nukes it. The message is stuck in outbox, any access to local folders will trigger message processing again leading to the 20GB+ RAM usage again. STEPS TO REPRODUCE 1. Attach a 779,5 MiB attachment to a mail in the composer. 2. Attempt to send the mail. OBSERVED RESULT The mail gets stuck in the local folders outbox and OOM will quickly follow. (Unless you have enough RAM, perhaps 100GB or so?) Every access of local folders will cause akonadi to re-read this mail, because it's stuck in the outbox, triggering the issue again and again. EXPECTED RESULT One of: a. It works without crashing or consuming a ridiculous amount of memory. b. It refuses to attach ridiculously oversized attachments. WORKAROUND If a mail with an extremely large attachment is stuck in the local folders, use "ncdu" or similar tool to locate the mail file on disk. For example "ncdu ~/.local/share/akonadi_maildir_resource_0". Then, stop akonadi, delete the problematic file and start akonadi again. RECOMMENDED FIX Set the composer setting "Maximum Attachment Size" somewhere between 50MB and 100MB or so by default. Then also either disallow unlimited attachment size completely or add a gigantic warning regarding the memory usage if set to unlimited. SOFTWARE/OS VERSIONS Kontact 5.9.3 (18.08.3, Debian Buster/Stable) Operating System: Debian GNU/Linux 10 KDE Plasma Version: 5.14.5 Qt Version: 5.11.3 KDE Frameworks Version: 5.54.0 Kernel Version: 4.19.0-6-amd64 OS Type: 64-bit ADDITIONAL INFORMATION See the attachment for htop output just before system unresponsiveness due to swapping and OOM killer invocation. Personal note: Although it may seem silly trying to try and attach a gigantic file to an email, I've seen this bug in production. Dragging & dropping a large LibreOffice presentation from Dolphin into Kontact is easily done, and the user's Kontact/akonadi is completely crippled afterwards if the file size happens to be in the "sweet spot".