mail                     | Jul 28 09:51:55 mail postfix/smtpd[2658]: warning: cannot load 1024-bit DH parameters from file /etc/postfix/dhparams.pem -- using compiled-in defaults
mail                     | Jul 28 09:51:55 mail postfix/smtpd[2658]: warning: TLS library problem: error:0906D06C:PEM routines:PEM_read_bio:no start line:../crypto/pem/pem_lib.c:686:Expecting: DH PARAMETERS:

root@mail:~# cat /etc/cron.d/dh2048
@weekly FILE=/tmp/tmp.aFRqiZNPZT ; openssl dhparam -out  2048 > /dev/null 2>&1 && mv -f  /etc/postfix/dhparams.pem
root@mail:~# echo "@weekly FILE=\`mktemp\` ; openssl dhparam -out \$FILE 2048 > /dev/null 2>&1 && mv -f \$FILE /etc/postfix/dhparams.pem" > /etc/cron.d/dh2048
root@mail:~# cat /etc/cron.d/dh2048
@weekly FILE=`mktemp` ; openssl dhparam -out $FILE 2048 > /dev/null 2>&1 && mv -f $FILE /etc/postfix/dhparams.pem