For FortiMail units operating in server mode as a config-only HA group, you must store mail data on a NAS server instead of locally. If mail data is stored locally, email users’ messages and other mail data could be scattered across multiple FortiMail units.

Even if your FortiMail units are not operating in server mode with config-only HA, however, storing mail data on a NAS server may have a number of benefits for your organization. For example, backing up your NAS server regularly can help prevent loss of mail data. Also, if your FortiMail unit experiences a temporary failure, you can still access the mail data on the NAS server. When the FortiMail unit restarts, it can usually continue to access and use the mail data stored on the NAS server.

For config-only HA groups using a network attached storage (NAS) server, only the primary unit sends quarantine reports to email users. The primary unit also acts as a proxy between email users and the NAS server when email users use FortiMail webmail to access quarantined email and to configure their own Bayesian filters.

For a active-passive HA groups, the primary unit reads and writes all mail data to and from the NAS server in the same way as a standalone unit. If a failover occurs, the new primary unit uses the same NAS server for mail data. The new primary unit can access all mail data that the original primary unit stored on the NAS server. So if you are using a NAS server to store mail data, after a failover, the new primary unit continues operating with no loss of mail data.

For instructions on storing mail data on a NAS server, see “Selecting the mail data storage location”.