I do not know whether you have set it up correctly nor whether you use Pop or Imap. Lots of unknowns at this point. You need to provide info: What OS do you use? What version of Thunderbird are you using? Is this an imap or pop mail account ? Have you used yahoo to generate an app specific password which you use instead of the ussual password? If not then you need to create one: https://help.yahoo.com/kb/generate-manage-rd-party-passwords-sln15241.html Do you get any error message ? If yes - post an image of the error. What are current incoming and outgoing server settings - post an image or : Help > Troublshooting Information scroll down to 'Mail and News Accounts' section Post an image showing everything in that section. If this is a recent/new install of Thunderbird: Have you accessed the Firewall and set up Thunderbird program as 'allowed' ? If no, then please do this first. Is your computer using a VPN ? If yes, then servers do not like them because they expect your IP address - anything else ...well the servers think someone is attempting to hack the account so they block access. Options - switch off VPN or create a split tunnel for Thunderbird to use. Info on Imap: https://help.yahoo.com/kb/SLN4075.html Info on POP: https://help.yahoo.com/kb/SLN4724.html