Вообще версия WS уже давно EOL. Windows 8.1 в целом тоже EOL. Возможно превышено ограничение в 20 одновременных сессий при обращении к общим папкам Windows.

I haven't, I treat this as a last resort. Such things shouldn't happen. I've raised a ticket with tech support, and I'm awaiting their response. I suppose it may simply be the same 🤔 BTW - I'm also observing issues with Outlook macros I use and which till the update worked flawlessly. This confirms Kaspersky is to blame here I believe.

Have You tried to uninstall Kaspersky, and run a clean install again, this time with the new Kaspersky 21.23 installer?

When I click "Send" Outlook freezes and won't unfreeze. The only solution is to "hard close" it (kill the task), or - in some cases - restarting the program from the dialog. No Kaspersky warning is produced, no relative event in the log. After disabling Kaspersky add-in Outlook is back to normal. Re-enabling makes it crash again.

Welcome to Kaspersky Community. What do you mean with crash? Outlook executing stops or You can't send emails? Any warning from Kaspersky?

Earlier today my Kaspersky Plus got auto-updated to version 21.23.6.614. Since then the Outlook add-in makes Outlook crash every time I send an email. Using Outlook is simply impossible, which questions the Kaspersky's product value for mail security. If relevant, Outlook version is 2510 build 19328.20158. Is this a bug or is there some solution/workaround?

чтобы ее снять, нужно знать пароль, а он его не знает. Либо пароль мог быть установлен через KSC. Официальный путь - через техподдержку, если у вас есть такая возможность. Неофициальный через правку реестра. В сети можно найти как.

День добрый. "Кто-то" установил защиту паролем. Снимите ее в соответствующем пункте Настройки - Интерфейс.