1: For the user login the SMTP or SSL SMTP to send email,there is no need to RBL check the login IP. RBL should only check those not loggin.

2: For the SPF check result,"helo=" string is always the domain after the @,it is not the real value.

3: Access control blank issue-->already settled at 6.3 5979

4: DKIM Key size in bits better have 1024 and 2048,as most of the DNS support 1024 but not 2048,as the value too long. Just like port25.com,you can choose 1024 or 2048

Need new function:

As long as the server port 25,110,143 is open,you can see a lot of HELO/ELHO like: ylmf-pc,user and etc.they keep scanning the password.Better have function of list IPs,the server will never give them any response,just disconnect.