[Q&A] add info in mail

[hestiap]

What is a problem?

H,
I'd like to add info from syslog in an alert email (hostname, level)
A the present time, I've got to add the message info with
message "Message: %s\n"
message_out_keys message

Describe the configuration of Fluentd

<match alert.**>

              @type "mail"
              host smtp.uuuu.fr
              port 587
              user xxxx       # Use your username to log in
              password yyyy  # Use your login password
              enable_starttls_auto true  # Use this option to enable STARTTLS
              from kkkkk          # Set the sender address

              to "[email protected]"  # Set the recipient address
              subject "Alerte syslog"
              message "Message: %s\n"
              message_out_keys message

Describe the logs of Fluentd

No response

Environment

- Fluentd version: fluent-package 5.0.5 fluentd 1.16.6 (fa1cfbb0335e7751a2fd5547897ab611484ee000)
- TD Agent version:
- Fluent Package version:
- Docker image (tag):
- Operating system: Ubuntu 22.04.5 LTS
- Kernel version: 5.15.0-130-generic

[hestiap]

I answer to myself...
I've found this

subject Alert: %s - %s
subject_out_keys host,tag
message %s \n%s \n%s \n%s
message_out_keys host,tag,ident,message
time_locale UTC

I don't know what does "time_locale UTC"