Add "-t" sendmail flag as another option as the "sendmail" default command

That's an interesting idea. We should be careful though as the comment from Symfony\Component\Mailer\Transport\SendmailTransport says this:

     * The recommended mode is "-bs" since it is interactive and failure notifications are hence possible.
     * Note that the -t mode does not support error reporting and does not support Bcc properly (the Bcc headers are not removed).
     *
     * If using -t mode, you are strongly advised to include -oi or -i in the flags (like /usr/sbin/sendmail -oi -t)

Agreed! I guess, we should add this information to the description of the command (if possible).

Any progress with this?

I hit this also with a 24.04 LTS server. It will only become more frequent.

/usr/sbin/sendmail -t should likely be the default instead of -bs

Not sure if it makes a difference however I am using postfix, so the sendmail command is essentially a wrapper for postfix.