Hi everyone,

At the ISP, I have

Host Record -- autodiscover.mydomain.com

Host Record -- mail.mydomain.com

MX Record -- mail.mydomain.com

I dont have PTR Record & SPF Record for my exchange. Do i need these both records?

You probably can't have a PTR record because you likely don't own the IP range, your ISP does.  What's important is that there is a PTR record and it's correct.

An SPF TXT is not required but may help keep mail from your users from being treated as

Reverse pointer record yes you would like to have it probably you can ask your ISP to create one on their DNS box.

Secondly SPF creation will help to keep away from SPAM attacks, below is a quick article which will help you understand about SPF.

http://kb.kerio.com/product/kerio-connect/server-configuration/antispam/how-do-i-create-an-spf-or-caller-id-record-248.html

thanks alot

An SPF record won't do anything to prevent a spam attack.  It helps prove that the mail your users send is coming from a trusted source and won't be marked as spam.