SOGo offers multiple ways to access calendaring and messaging data. Your users can either use a web browser, Microsoft Outlook, Mozilla Thunderbird, Apple iCal, or a mobile device to access the same information.

SOGo is a highly interoperable solution due to its adoption and promotion of open standards. Among those, SOGo particularly focuses on:
CalDAV: The Calendaring Extensions to WebDAV protocol is vastly popular among clients (Apple iCal, Mozilla Lightning, etc.) and allows them to exchange calendar components with servers that support it.
CardDAV: In its fourth revision, vCard Extensions to WebDAV is to address books / contacts what CalDAV is to calendaring. Less popular than CalDAV, it's nevertheless quickly gaining momentum and is used by the SOGo Connector extension.
Mail protocols: For messaging, SOGo fully makes use of standard protocols such as IMAP and SMTP.