451 4.3.0 Temporary internal failure

[Nutsch]

Hi

i can send mails without problems in any direction, except when the 
attachments are bigger than 1 MB. I alway get this message

relay=mail.example.net[private/dovecot-lmtp], delay=35155, 
delays=35155/0.03/0.02/0.09, dsn=4.3.0, status=deferred (host 
mail.example.net[private/dovecot-lmtp] said: 451 4.3.0 Temporary 
internal failure (in reply to end of DATA command)) Aug  3 19:34:34 
46185 dovecot: lmtp(6477): Disconnect from local: Temporary internal 
failure (in DATA)


postconf message_size_limit
message_size_limit = 0
postconf mail_size_limit
mailbox_size_limit = 0

i can send big attachments to an extern address but not from intern to 
intern. Someone said that maybe the tmp directory is the problem so i 
checked the size.

ls -ald /tmp/; df -h /tmp/
drwxrwxrwt 4 root root 80 Aug  3 19:44 /tmp/
Filesystem      Size  Used Avail Use% Mounted on
-               1,0M  4,0K 1020K   1% /tmp
root at example:/tmp#

is there a connection between lmtp and the size of the tmp directory? 
And why is the size 1,0M, tmp is not an own partion. Should i increase 
the size? And if yes, how?

df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/vzfs        80G   12G   69G  15% /

???

br. noctua