TL;DR: Outlook performance degrades sharply when your PST file exceeds 20GB. The solution is to compact, split, or archive your data. Jump to Solution 3 to learn how to split your PST file safely. Few things test your patience like a sluggish Outlook—endless “Not Responding” messages, delayed send/receive, and random crashes. If your Outlook has … Continue reading Fix: MS Outlook Runs Slowly or Crashes – Oversized PST File Performance