I'm monitoring multiple mailboxes in Outlook and for this I open multiple Outlook windows so that I can easily switch between windows instead of needing to browse between folders. I usually have an additional Outlook window open for my Calendar as well.
I only found an option for a single startup folder. I guess I'm looking for an option similar to Internet Explorer where I can set up multiple Home Page folders or restoring my last browser session.
Is there anything similar in Outlook so that I can open all these folders automatically at startup?
Outlook does has something similar to this indeed but it is not directly configurable as a feature.
Instead of closing all your Outlook windows in order to close Outlook, choose File-> Exit instead.
Outlook will now remember all the folders that you had open at the time of closing Outlook and will reopen them when you launch Outlook again.
Note: It will only remember the open folder windows. Outlook will not remember and reopen any message or other item window that you had open at that time.