mountain lion server

I'am not happy with email on my brand new Mountain Lion Server, because Mail is interupted once a day.

After some research I've found a full Mail Queue:

bash-3.2# mailq

-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------

6AC592A5200 31822 Fri Oct 19 18:29:22 x@x.xx

(host 127.0.0.1[127.0.0.1] said: 421 4.3.2 Service shutting down, closing channel (in reply to MAIL FROM command))

y@y.yy

6F1FF2A6400 5906 Fri Oct 19 19:31:19 x@x.xx

(host 127.0.0.1[127.0.0.1] said: 421 4.3.2 Service shutting down, closing channel (in reply to MAIL FROM command))

y@y.yy

772B62A6200 7503 Fri Oct 19 19:20:50 x@x.xx

(host 127.0.0.1[127.0.0.1] said: 421 4.3.2 Service shutting down, closing channel (in reply to MAIL FROM command))

y@y.yy

86DAB2A6100 11014778 Fri Oct 19 19:12:08 x@x.xx

(host 127.0.0.1[127.0.0.1] said: 421 4.3.2 Service shutting down, closing channel (in reply to MAIL FROM command))

y@y.yy

8F4182A6200 45315 Fri Oct 19 19:19:39 x@x.xx

(host 127.0.0.1[127.0.0.1] said: 421 4.3.2 Service shutting down, closing channel (in reply to MAIL FROM command))

y@y.yy

-- 12973 Kbytes in 10 Requests.

after some further inverstigations I've found out, that amavisd has some access problems with a temporary directory:

bash-3.2# tail -f amavis.log

Oct 19 19:25:31 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[78982]: (78982-01) (!!)TROUBLE in process_request: Error in tempdir() using /Library/Server/Mail/Data/scanner/amavis/tmp/amavis-20121019T192531-78982-XXXXX XXX: Parent directory (/Library/Server/Mail/Data/scanner/amavis/tmp) does not exist at /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd line 5987

Oct 19 19:25:31 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[78982]: (78982-01) (!)Requesting process rundown after fatal error

Oct 19 19:25:32 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79091]: (79091-01) (!!)TROUBLE in process_request: Error in tempdir() using /Library/Server/Mail/Data/scanner/amavis/tmp/amavis-20121019T192532-79091-XXXXX XXX: Parent directory (/Library/Server/Mail/Data/scanner/amavis/tmp) does not exist at /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd line 5987

Oct 19 19:25:32 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79091]: (79091-01) (!)Requesting process rundown after fatal error

Oct 19 19:28:19 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79090]: (79090-01) (!!)TROUBLE in process_request: Error in tempdir() using /Library/Server/Mail/Data/scanner/amavis/tmp/amavis-20121019T192819-79090-XXXXX XXX: Parent directory (/Library/Server/Mail/Data/scanner/amavis/tmp) does not exist at /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd line 5987

Oct 19 19:28:19 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79090]: (79090-01) (!)Requesting process rundown after fatal error

Oct 19 19:30:08 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79092]: (79092-01) (!!)TROUBLE in process_request: Error in tempdir() using /Library/Server/Mail/Data/scanner/amavis/tmp/amavis-20121019T193008-79092-XXXXX XXX: Parent directory (/Library/Server/Mail/Data/scanner/amavis/tmp) does not exist at /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd line 5987

Oct 19 19:30:08 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79092]: (79092-01) (!)Requesting process rundown after fatal error

Oct 19 19:31:19 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79195]: (79195-01) (!!)TROUBLE in process_request: Error in tempdir() using /Library/Server/Mail/Data/scanner/amavis/tmp/amavis-20121019T193119-79195-XXXXX XXX: Parent directory (/Library/Server/Mail/Data/scanner/amavis/tmp) does not exist at /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd line 5987

Oct 19 19:31:19 mmini.de /Applications/Server.app/Contents/ServerRoot/usr/bin/amavisd[79195]: (79195-01) (!)Requesting process rundown after fatal error

after issuing the following commads in "/Library/Server/Mail/Data/scanner/amavis"

bash-3.2# mkdir tmp

bash-3.2# chown _amavisd:_amavisd tmp

bash-3.2# postqueue -f

everything is working fine again, but for how long?

Has anybody a good explanation for this strange behavior?