Outlook 365 Preparing outlook for first use, Loading mailbox settings

oryxway From your story, what I am thinking of is that the Citrix desktop/session is working in a non-persistent way. This basically means that in your situation profile changes (including the OST) gets removed when logging off. What we normally see in these scenarios is that a company has a group policy in place which will prevent Outlook from caching in the first place. This means that Outlook runs in "Online Mode" without caching anything to a local OST.

Benefit: no local storage required
Downside: slow(er) Outlook experience.

There are however tools which can overcome this issue like FSLogix.