Reasons Microsoft email clients lose files

Both of these email clients (a client is the side of the program on your computer) manage to prolifically lose emails, necessitating email recovery, for the following reasons.

For some reason when Outlook emails are compressed and unzipped the files suffer data loss. Lose enough 0s and 1s and before long the email you were saving will no longer open.
When an Outlook or Outlook Express email is downloaded, it is often scanned by a local antivirus program. These programs occasionally alter the structure of the message and as a result damage its files. The file then disappears and you are left wondering where it went.
Various versions of Microsoft Outlook have specific size limitations on how much mail can be archived in the folder. Should you exceed that limit files essentially spill out of the folder and are lost.
And, of course accidental deletion of emails. Everyone who has ever used a computer has accidentally deleted a wanted file. Emails are deleted more than any other file type because we tend to quickly scan over the latest mail and discard spam and other unneeded documents.