There's a difficulty here; Microsoft re-brand and re-launch their email products periodically, so we can't be sure what you mean by an "outlook account". It could mean the system previously known as hotmail/msn/outlook.com which are essentially webmail with POP and SMTP support and can easily be made to work in a regular standards-compliant email client such as Thunderbird. (OTOH, if you're talking about an account hosted by an MS Exchange server then it's a slightly different problem and can be more complicated to set up, depending on which facilities have been enabled by the operator of the server. It may not have regular POP/IMAP/SMTP protocols that Thunderbird needs.) Does your password include any non-alphanumeric characters? Some characters which may work in webmail via http aren't permitted in the POP and SMTP protocols, so a password which works with the website may not work in email. Firewalls can cause difficulties too. You can try this: go to '''[http://kb.mozillazine.org/Menu_differences_in_Windows,_Linux,_and_Mac Tools|Options]|Security|Passwords→Saved Passwords''' and delete any stored passwords for this account. Or this: setting up the account in Thunderbird again might get you past problems caused by an incomplete setting-up.

If it's an outlook/live/hotmail account, make sure that two-step verification isn't causing the problem: https://support.mozilla.org/en-US/questions/1005967