shoaib
So the problem is elsewhere. I hope I can find a solution soon.
You have totally misunderstood what I was advising you.
The problem is not with your ISP, and as you deduce the problem is elsewhere.
It is with yahoo, hotmail, and gmail.
They are the ones blocking your sme smtp server from connecting to their smtp server.
The error message clearly says that.
ie
Sorry,_I_wasn't_able_to_establish_an_SMTP_connection.
The blocking is NOT as a result of your sme server IP being on any RBL lists, I never even mentioned those.
As I said, yahoo, hotmail & gmail use special algorithms to deduce the likelihood of your servers IP being that of a spammer.
You will need to contact those ISP's tech support people to have your servers IP listed on their exclusion list. Have a look on their support websites.
OK then, if you have Reverse DNS/PTR records setup then that part is OK.
What about Sender Policy Framework (SPF) records for your domains ?
You will get blocked if you don't have that setup.
I have been through all this, and the ultimate answer is to get your server listed on the exclusion lists maintained by yahoo, hotmail & gmail. But they will not list you until you conform to all their requirements and provide (for example) information about the path your server takes to talk to their servers etc etc and verify that you have put in place certain requirements eg PTR & SPF etc. See their tech support websites for details of the information they want from you.
Search for technical support for system administrators for each of those providers.