qmail + Solaris 7.0 fatal: data 451 qq write error or disk full (#4.3.0)

[Michael Maier]

Someone knows why I get fatal: data 451 qq write error or disk full
(#4.3.0) ?
It comes after different Message Counts when sending via SMTP.
I think there is an Error in that qmail-smtpd. Any Solutions ?
Never seen that on Linux btw.
--
Michael..