vCenter Server Email Alerts Fail to Deliver During Network or Switch Outage/ Maintenance Events

Products

VMware vCenter Server

Issue/Introduction

No email alerts are received during a known network maintenance window (e.g., core switch reboot, cable upgrades).
No alerts found under triggered alarms in the vSphere Client.

In vCenter journalctl logs show: vCenter detected the outage and even tried to send SNMP traps . However, when it attempted to open a mail connection to send the email, the network path was unavailable due to the maintenance, resulting in the 'AlarmEmailFailedEvent' error.

MM DD HH:MM:SS ##vCenter_FQDN##  vpxd[6168]: Event [8460539] [1-1] [YYYY-MM-DD T HH:MM:SS] [vim.event.EventEx] [info] [] [####### ####] [8460539] [Alarm 'Host connection failure' on ##ESXi_HOST_NAME## triggered by event 8460485 'Host_ESXi_NAME in ############ is not responding']
MM DD HH:MM:SS ##vCenter_FQDN## vpxd[6168]: Event [8460545] [1-1] [YYYY-MM-DD T HH:MM:SS] [vim.event.AlarmSnmpCompletedEvent] [info] [] [####### ####] [8460545] [Alarm 'Host connection failure': an SNMP trap for entity ##ESXi_HOST_NAME## was sent]
MM DD HH:MM:SS ##vCenter_FQDN## vpxd[6168]: Event [8460546] [1-1] [2026-01-18T15:09:54.858188Z] [vim.event.AlarmEmailFailedEvent] [error] [] [70 #####] [8460546] [Alarm 'Host connection and power state' on ##ESXi_HOST_NAME##  cannot send email to [email protected];[email protected]]

Environment

VMware vCenter Server
VMware vSphere ESXi

Cause

This issue occurs because of a dependency in the network architecture. When vCenter Server detects a host failure (e.g., Host connection lost) during network maintenance/ outage the SMTP server needs to be reachable else the mail gets queued and drops due to timeout;
- Detection: vCenter Server successfully identifies the host outage and triggers the alarm action.
- Action: vCenter attempts to send an email notification via the configured SMTP server.
- Failure: Because the core switches or uplinks are undergoing maintenance, the network path from vCenter Server to the SMTP server is severed.
- Result: The email transmission times out or fails with "Network Unreachable," and the alert is never delivered.

Resolution

Ensure Management Network is stable since vCenter relies on this to reach the mail server and deliver the triggered alarms.
Verify the mail configuration is correct and perform a 'Safe Test' following below steps:

- Create a temporary, sensitive alarm to validate the email mechanism works.
  - Right-click your 'Datacenter' or a specific Cluster in the inventory and select Alarms > New Alarm Definition.
  - Name and Target:
    - Name: _TEST ADMIN ALERT (Using _ keeps it at the top of the list).
    - Target Type: Virtual Machine.
    - Click Next.
  - Alarm Rule (The Trigger):
    - Find the logic line: "IF [argument]".
    - Click the dropdown and select VM Powered On. (This means the alarm fires every time you turn on a VM).
    - Click Next.
  - Alarm Rule (The Action):
    - Under Reset Rule, leave as default. Click Next until you reach Review/ Configure Actions.
    - Select Send a notification email.
    - Configuration: Enter your email address in the box.
    - Subject: TEST - vCenter Email Triggered.
    - Frequency: Select "Once" (to avoid spamming).
  - Enable: Ensure the "Enable this alarm" toggle is ON.
  - Click Create/Finish.
- Trigger the Alarm:
  - Find a Test VM (or a non-critical VM) that is currently powered off.
  - Right-click the VM -> Power -> Power On.
  - Wait 10–30 seconds.
- Verify the Results:
  - Check the vCenter UI under Monitor> Issues> Triggered Alarms.
  - Check your Email Inbox for the email.
- If the alarm triggered in vCenter but no email arrived, collect the vCenter logs and reach out to Broadcom Support.
- Once the test is successful:
  - Go back to Alarms > Definitions.
  - Select _TEST ADMIN ALERT.
  - Delete it so you don't get emailed every time a VM turns on.

Additional Information

Reference documentation to Configure Mail Sender Settings.