Just a quick note,
This technique is possible on 5.0.9+ but there are several reasons to only use it on 5.0.10+:
We found that minor mail store corruptions like a missing blob, size mismatch, or 0 byte db entries can cause a tar operation to halt prematurely/you’ll notice missing data.
You can determine if that is the problem by running “tar tfz account.tgz” and verifying that the listing completes without a corrupt stream error message.
This is similar to bug 31937 (another error handling one was bug 31016) - a fix for truncating or padding mismatched blobs will be included in 5.0.10 NE & we currently plan to release an updated 5.0.10 FOSS as well.
ZCS-to-ZCS Migrations » Zimbra :: Blog