For the past 2 months I've been using this Thunderbird android app. I don't understand why I keep getting multiple mails being received in my inbox of gmail and Yahoo accounts. I request you to kindly look into this matter. Rest all good with the email client.

I must admit that I use another mail client 'Aquamail' too. I have those same set of multiple email accounts wherein I receive the intended one, not more than one mail.

I've thoroughly checked and adjusted the settings of the Thunderbird client.

I hope the developer will find and offer the solution for it.

If anybody else too faced such and solved it, please let me know. Thank you.

Are you using a pop3 connection with your email provider's setting "leave a copy on the server" enabled? This might explain it.