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"Version 5" is db3.x, "Version 8" is db4.x. Confused yet? Don't blame us, we only work here. You need to install db3-utils to get the "db3_load" command to save in a format that the DB_File module (and therefore SpamAssassin) can use.
(On Debian, don't install an older "-dev" package, like "libdb2-dev", as it'll override the newer stuff. You just need "libdb2" and "libdb2-utils" or similar.)
Other Dbs
You can do the same with the bayes_seen and auto-whitelist files, but they're not as important; I generally just blow them away:
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