Why does Outlook show the error code 0x80040900?

It happened to me one morning — I opened Outlook, and instead of my inbox, I got the error “0x80040900”. It turns out, this happens when Outlook can’t communicate with the mail server, often due to incorrect POP/IMAP settings, damaged PST files, or unstable network connections. I double-checked my server settings and restarted Outlook — still no luck. The real issue was a corrupted PST file. Thankfully, I used the DRS PST Recovery Tool, which fixed the file in minutes and restored my emails without affecting data integrity.