This is not a Thunderbird issue. The error you are receiving is a security check enforced by Gmail, but not uniformly by others. So, while you may be able to email other email providers, you cannot send to Gmail addresses. The error is that your domain name is not properly documented as being identified with the IP address you are using. You need to work with your domain registrar and/or your email host provider to resolve this.

I have successfully integrated my email account into Thunderbird, but I am experiencing an issue where I am unable to send messages to Gmail email addresses. Emails are received without any issues, but when I attempt to send a message to a Gmail address, it doesn't go through. Please guide me about it.

I suggest sharing the message with your email provider, as the message states what needs to be changed. The work is to be done on the server, not in Thunderbird, and only people supporting the server can do this.