Basically I need good hosting on Linux with Professional Email Software.

I am here in India running my reseller hosting business, But my clients that
are on Linux Server, mostly uses, online email panel for sending & receiving emails.

But from there feedback, they are not satisfied with the online system of emailing. So to overcome this problem, what you suggest me.

Kindly suggest me. Related to pricing I am open, but let me know the
best possible solution with best optimised price.

With Regards.