The first time that a user signs in to Outlook Web App, the user has to set his or her current time zone. If the user doesn't set the time zone, the time zone is set to (UTC) Monrovia, Reykjavik. There's no method for admins to set up the time zone setting in advance in Outlook Web App for all users.
The following screen shot shows the Outlook Web App sign-in screen in Office 365.
- Sign in to Outlook Web App, click Settings (), and then click Options.
- In the left navigation pane, click Settings, and then click Regional.
- In the Current time zone box, click the arrow, and then click the correct time zone setting.
- Click Save.
For more information about incorrect time zone information in read receipts, see the following Microsoft Knowledge Base article:
Article ID: 2298834 - Last Review: Dec 16, 2016 - Revision: 1