Quoting Joachim Fahrner (jf@???):

> That's right. And my local unbound is the only nameserver in
> /etc/resolv.conf
>
> I cannot use other nameservers because my postfix queries some RBLs
> that allow only limited numbers of queries (they are free for
> personal use, but costs for commercial use).

I'm a big fan of running a local recursive nameserver, and of Unbound.
So, in general terms, I certainly encourage your approach. It's not
obvious from present evidence why you are getting timeouts querying your
local recursive nameserver. You'll have to do further diagnosis
locally. (Lacking any better ideas at the moment, I'd say maybe start
by looking at Unbound's log files.)

You _could_ add some additional recursive nameservers (like perhaps your
ISP's) on additional lines below the 'nameserver 127.0.0.1' one --
knowing that they'll be used only if your Unbound instance for some
reason isn't responding.