Troubleshooting Tip: Persistence issue with exchange connections using the source IP

Description

This article describes a persistence issue with exchange connections while using source IP as persistence method. Causing emails to get stuck in the outbox due to inconsistent load balancing between exchange servers.

Scope

FortiWeb.

Solution

To resolve the persistence issue with exchange connections using the source IP, follow these steps:

1. Navigate to Server Policy -> Server Pool and select the pool that is experiencing the issue.

2. Increase the Source-IP persistence timeout to 2800 seconds. This will ensure that the persistence entry does not expire too quickly, causing the issue.

According to the Microsoft article Session timeouts for Microsoft 365, OWA sessions are designed for long-lived web sessions (multiple hours long), so increasing the persistence timeout is considered a safe margin.

Monitor the issue after making the changes to ensure that it is resolved.

It is recommended to use persistence cookie instead of source IP, as cookie persistence is generally more application-aware. However, if the issue still persists, increasing the source-IP persistence timeout can help resolve the issue.

Related document:
server-policy persistence-policy