1.  We do not accept mails if senders mail server ip is black listed in above site.

2. We do not accept mails if senders domain is failed to verify.

3. we do not accept mails if mails coming from invalid or forged headers or on-existent domain names

4. User base filter 

  i)  we block  message to the that user if he has blocked some domain or email id from webmail.
  ii) we block  message to the that user if he has put some key words in his filter list based on subject or body of message using webmail.

5.  We do not accept addresses with local parts that contain any of the characters '@', '%', '!', '/' or '|'. 

6. We expect HELO/EHLO  with a valid domain at beginning of SMTP talk otherwise reject.

7. If message body contain following key words then reject the message ( Obsolate)
Viagra, "Approve Me Now!" , "Your medication is on it's way. No prescription required!" , "V-i-a-g-r-a" ,"V-i-a-g-r-a?" , "v-i-a-g-r-a" , "v-i-ag-r-a" , "v-ia-g-r-a" , "vi-a-g-r-a" , "via-g-r-a", "viag-r-a" , "Via*gra*","viagra?" , "Penis Enlargement", "mortgage" etc

8.  We don't accept if message contains an attachment with following extension

exe:com:vbs:pif:bat:scr:ade:adp:bas:chm:cmd:cpl:crt:hlp:hta:inf:ins:isp:js:jse:lnk:mdb:mde:msc:
msi:msp:mst:pcd:reg:sct:shs:shb:vb:vbe:vbs:wsc:wsf:wsh

9. We also maintain local database to block various domain/IP address/Network email id for various reasons.  

10. We declare SPF records and  allow only emails from SPF declared hosts for that domain if any.

11. we accept relay only when MX of the domain pointing to us.

12. we do not check RBLS if relay is open or sender is authenticated by smtp-auth for outgoing mail server.

13. we Reject messages that carry Chinese character sets.

14. we frozen message if the message lies more than 3 days in the queue for any reason.

15. we have also  a "score tally" system where large numbers of inter-related rules fire off and total up a score to determine if a message is spam or not. The whole system operates by trying to balance the most spam and nonspam each on the right side of the 
threshhold. 

16. If theshhold is  > 9 we permanently reject the message saying classified as SPAM.

17. if threshold is > 8.0 and < 9.0 we temporally reject the message and and accepted in next retry and marked as [**Likely SPAM] 

18. if threshold < 9 and > 3.0 we accept the mail and notify recipient by rewriting subject tag as [**likelySPAM] . 

19. we also maintain white-list database to bypass above policy for some authentic domains/networks.

20. Any domain taken email service from us we put  in whitelist to avoid spam checking while sending.

21. We don't check for spam if customer using our smtp server of us or any domain which mx is pointing to us.

22. we allow  spam in abuse & support & postmaster ID.