I have configured to make the mails from my company mail id to be retrieved in my Personal mail address(gmail). Here I dont know is there any possibility for my management members to access my Personal mail. Before they have configured my company mail id in thunderbird.
If your company IT department set up your Thunderbird for you, using your username/password, then they definitely have full access to your account. Even if you entered your own login details, if this was set up on your work-owned computer then they might have remote access to the machine whenever they want, so they could still view and send/receive from your account.
I tend to think it's best to keep work and personal accounts separate, and this is a pretty good example of why. You also might have certain contractual obligations to give up any work-related data/emails/contacts when you leave the company, so having these in your personal accounts really muddies the waters.