Server Mail Settings moved to System Settings
The system-wide Mail Settings for DXP were migrated to use the standard system configuration framework.
The system options in Server Administration > Mail were moved to System Settings > Email > Virtual Instance Scope > Mail Settings
The existing settings from previous releases will be automatically migrated during the database upgrade process.
The following portal properties were removed since they are now defined by configuration properties:
LIST OF PROPERTIES
Following standard configuration patterns, Instance Settings > Email > Mail Settings will have default values inherited from the System Settings. The administrator for Portal Instances can now view the default values, override, or reset to default.
Please refer to Configuring Mail - Liferay Official Documentation for additional details.