I'm having trouble figuring this out from any of the documentation or website pages: is dovecot v1.0 considered to be stable,

Depends on your definition... read the archives, this question has come up before. The consensus is, please, no more prodding, let Timo release it as 1.0 when it is ready...

or is it still testing/beta?

It is currently at rc24 (I know - but there were two periods where certain changes introduced certain issues that caused instability for some people, but it is probably a good thing, because Timo found and fixed many long-standing bugs... it is actually very stable for me now, and the performance has increased quite a bit as well.

If the latter, is there any timeline for a "stable" release?

When it is ready... ;)

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Best regards,

Charles