If you want to respond to an email with a simple "Ok" in a gentle and polite manner, consider adding a bit more context to your response to make it feel more complete. Here's a polite way to do it:
Subject: Re: [Subject of the Email]
Dear [Sender's Name],
Thank you for your email. I've reviewed the information, and I want to let you know that everything looks good to me. So, consider this my confirmation: "Ok."
If you have any further questions or need any additional input, please don't hesitate to reach out.
Best regards, [Your Name]
By providing a brief acknowledgment and expressing your appreciation for the email, you add a courteous touch to your response while keeping it concise. This way, you let the sender know that you've understood and accepted the information without sounding dismissive.