p/s if you tried setup with 3th party apps for send notification via gmail, this guide might suit too.
Current my analyzer running 5.2.5
Herewith the steps
1. Setup on Fortianalyzer mail server setup
for information about gmail setting
2. SSH to Fortianalyzer , configure the secure option, this command make sure using starttls.
config system mail
set secure-option starttls
below is the wireshark capture using starttls, as the red arrow indicate the SSL handshake start
3. Login into your gmail account
4. Access the url https://www.google.com/settings/security/lesssecureapps , turn it on
You can skip steps 5 and 6 if you 1st time setup gmail smtp server, else continue
5. Access the url https://accounts.google.com/DisplayUnlockCaptcha, click continue
6. You will come to this page below
6. Let test the email setup, right click the email setup and key in the recipient email
7. You should successfully send the email