A misconfigured certificate or expired security setting can throw up an Outlook Security Certificate Error and block your email flow. This write-up highlights common causes and suggests what to check before moving on to deeper fixes. When the certificate issue has already disrupted your mailbox data, the MSOutlookHelp PST Repair tool can fix the corrupted PST file behind the scenes. It recovers items with original metadata things like sender, date and subject intact, helping your restored mailbox look just like before. It also works with large PST files, so even heavy archives get repaired without slowdowns.