i have a single site which is on ssl and your realy simple ssl plugin installed on it.everything is working fine but when i add a post, and inside post i add any external url of website which is non https, it also redirects it to https and in result the external website url is not opening. Please suggest a solution for it.
Does it also happen when you disable the mixed content fixer in settings/ssl?
I have seen this only once, and in that case it appeared to be another plugin. What is your domain and the external link?
the mixed content fixer is designed not to replace external hyperlinks, so it would be very strange indeed. But it is of course possible that on certain edge cases the regex does not work properly. We can check that if you disable the mixed content fixer.
If the issue is still there when the mixed content fixer is disabled, it is not caused by Really Simple SSL. I would try deactivating your other plugins one by one to see if any of them is causing the issue.