I configured KMail in a new system installation, to use sendmail to send mails. However, mails failed to send until after a system restart.
STEPS TO REPRODUCE
1. Install and configure postfix as a sendmail mechanism. I tested that this was working by successfully sending emails via the command line.
2. Use KMail's settings dialog (Accounts section, Sending tab) to set up a sendmail transport. This was the first and only sending method which I configured.
Attempting to send emails using KMail always failed. They just remained in the outbox. No error messages.
Using akonadiconsole, I restarted the Mail Dispatcher Agent. This made no difference.
Following a system restart overnight, mails now send successfully.
It should not require a system restart in order for this configuration to start working. Whatever it was that needed to be reset by a system restart should automatically be done without user intervention, as soon as a sendmail transport is configured by the user.
This wasted quite a bit of time investigating the issue yesterday. This bug might prompt some people to abandon their attempt to use sendmail and switch to another method.
Linux/KDE Plasma: Debian 11
(available in About System)
KDE Plasma Version:
KDE Frameworks Version: 5.78.0
Qt Version: 5.15.2