We recommend all 4.5.2 users upgrade immediately to this release.
The 4.5.3 release fixes a number of bugs in 4.5.2. The impact of bug 14984 was that incoming 8 bit messages could be permanently corrupted when they enter the ZCS. This has impacted several customers outside the United States, and customers anywhere receiving mail from people outside the United States. This major bug existed only in 4.5.2 and is fixed in 4.5.3. We also believe that the periodic issues with the web client failing to load in IE7 have been fixed. Please provide feedback on this via support or bug 12318. Please see the release notes for full details.