GRR can't send email using SMTP

Environment

GRR from release DEB
GRR version 3.4.7.1
the GRR server run on Ubuntu 22.04
GRR client run on Windows 10

Describe the issue Hello, I just having trouble for sending email using SMTP. It says STARTTLS is not supported in your server. Can you explain to me the trouble and what step for fixing it?

Thank you

Error logs

ERROR:2024-01-12 03:02:46,446 45769 MainProcess 140626681198144 flow_processing_pool-845039062 flow_base:582] Error in flow 454F3DE7B98DFA65 on C.ec9fe6daf8c216a9: Could not connect to>
  File "/usr/share/grr-server/lib/python3.10/site-packages/grr_response_server/email_alerts.py", line 139, in SendEmail
    s.starttls()
  File "/usr/lib/python3.10/smtplib.py", line 771, in starttls
    raise SMTPNotSupportedError(
smtplib.SMTPNotSupportedError: STARTTLS extension not supported by server.

google / grr

GRR can't send email using SMTP #1053