amavisd 的key size

# amavisd -c /etc/amavisd/amavisd.conf testkeys
TESTING#1 mydomain.com: dkim._domainkey.mydomain.com => fail (OpenSSL error: data too small for key size)

# amavisd -c /etc/amavisd/amavisd.conf showkeys
; key#1 1024 bits, i=dkim, d=mydomain.com, /var/lib/dkim/mydomain.com.pem
dkim._domainkey.mydomain.com.   3600 TXT (
  "v=DKIM1; p="  "MIGfMA0GCSqGsIb3DQEBAQUAA4GNADCBiQKBgQC+5GTYBsiC8lDtw0UW9NQ3QOme"  "Xz4h3ebaA5NqQpNc+JnRQjJZ3KGTotqILNnMaPIcM1eR+AFF9Hx2z7ktXx0LdlGa"  "EQKkt6X3yFkL31Z935bXyk+nV22YrFF0HmCkba7vg8NMNoseOIQe7dZSnSExZw1m"
  "qcAtXYT8Y/1b4h5g7QIDAQAB")

iRedMail 預設安裝1024 , 是否修改2048?

Thanks.