Please can some one here help me on how i could block spam from coming to my mail server I use mikrotik as the firewall for the email server and do dst and src nat for the mail server. Thank in advance
this is done in the mailserver. routeros knows nothing about emails.
configure mailscanner in your mailserver.
ask google about spamassassin
and this is NOT routeros related. 
Thanks for all the reply am looking forward to a way out thanks all
I know it is is OT but I’m using this and almost all spam has gone, it is free and runs in vmware server which is also free!
it’s the same spamassassin/mailscanner that me and janisk mentioned above. just in a readymade package.
precisely - it is ready to use for those of us not wanting to become email server experts.
As requested here http://forum.mikrotik.com/t/feature-request-network-blacklists/9742/1 the ability to import IP blacklists into a firewall rule would help fight spam and general malicious traffic.
ngds…if you are bored…or have time..u can do what i did and use *nix scripts + grep + telnet to automate that IP black to firewall list process…but i agree it would be nice to have a cleaner way to import rules..
but there is a way now…