FortiGate 601E v7.4.12 - Email-based SSL VPN Two-Factor Authentication generates OTP event but never sends SMTP traffic

Fortinet TAC has also reviewed the case and confirmed that they cannot see any SMTP traffic leaving the FortiGate.At this point, it appears that the email notification process is never invoked even though authentication reaches the "Token is needed" stage.

Hi everyone,

I am facing a very strange issue on a FortiGate 601E running FortiOS 7.4.12 (build 2902).

Environment

- FortiGate 601E
- FortiOS v7.4.12 GA build 2902
- Multi-VDOM enabled
- Root VDOM hosts the SSL VPN
- SSL VPN authentication uses Local User + Email-based Two-Factor Authentication

Symptoms

The SSL VPN login works normally.

After entering the username and password, the SSL VPN client displays:

"An email message containing a Token Code will be sent..."

The System Event log also records:

"Send two-factor authentication token code"

However, the user never receives the email.

What makes this strange is that FortiGate never attempts to establish any SMTP connection.

Troubleshooting performed

✓ Local user configured with:

set two-factor email

✓ Email address configured correctly

✓ Email server configured

SMTP Server:
fortinet-notifications.com

Port:
465

Security:
SMTPS

✓ Custom Email Settings enabled

✓ Email server source interface configured

config system email-server
    set interface-select-method specify
    set interface "port1"
    set source-ip <Public IP>
end

✓ FortiGuard source interface configured

config system fortiguard
    set interface-select-method specify
    set interface "port1"
    set source-ip <Public IP>
end

✓ Default route verified

✓ Public DNS configured

✓ Internet connectivity is working

✓ SSL VPN works normally

✓ System Event shows:

"Send two-factor authentication token code"

✓ fnbamd debug confirms:

Local authentication SUCCESS
Token is needed
Sending result 7

No authentication failure is present.

Most importantly:

Running packet sniffer:

diagnose sniffer packet any "tcp port 465" 6 0 l

shows absolutely NO packets during the login attempt.

Also,

diagnose sniffer packet any "host fortinet-notifications.com"

shows no traffic.

The SMTP process never appears to start.

Question

Has anyone experienced this on FortiOS 7.4.12?

Is there any known bug where Email-based Two-Factor Authentication generates the event log but never invokes the alertmail process?

Any hidden debug command for alertmail would also be appreciated.

Thank you.