We need more details.

When posting a question - the section where enter details does not mean repeat the question. So the following are the details you needed to supply in order for people to understand what you are using and what is the problem and accompany that with relevant dta and images as necessary.

1. What Operating System you use..Windows 10 , MAC or Linux ?
2. What version of Thunderbird are you using ?
3. Are you talking about a POP or IMAP account ?
4. If you are getting an error message then post an image of the error message or type it word for word.
5. Do you have a problem with receiving or sending or both ?
6. Logon to webmail account via a browser and confirm your password works.
7. Whilst logged on to server - are you seeing new mail on the server ?

Post the following data:

• In Thunderbird
• Help > Troubleshooting Information
• scroll down to 'Mail and News Accounts'
• Copy all the data and paste it into a reply box int his forum OR post an image showing details.