I use Mozilla Thunderbird and have several addresses with one email provider

Nice to meet you, *****!
So you are not receiving the emails on one of your email accounts in Thunderbird?

What do you mean by "not loading"?

Got it.
Let's try to repair your inbox folder.
Open Thunderbird and select the folder in which the email is present which you want to view.
Next, right-click on the selected folder and choose the Properties option.
Now, you will see the Repair Folder button in the Folder Properties. Click on the Repair Folder > OK.
After the completion of the repair process, try to open and view the emails again.

Got it.
Let's Rebuild Folders in Mozilla Thunderbird.
Before implementing the steps, make sure that Thunderbird is closed and is not running in the background.
Here are the steps:

1. Open the location similar to: C:Users<Username>AppDataRoaming
   ThunderbirdProfilesxxxxxxx.default-release
2. Go to the data folder i.e., ImapMail or Mail folder as per your account configuration.
3. If the problem is with your Inbox, carefully delete the Inbox.msf file.

Got it.
It should be in ImapMail or Mail folder.

Got it.
Now, restart Thunderbird. It will rebuild the MSF file and show all the messages.

Are you sure that you deleted the needed file?

Ok.
Did you close Thunderbird before deleting the file?

Got it.
Did you terminate the background processes?

Hold on. Did you double-check that the needed file was removed?

Ok. Please start Thunderbird and try checking your inbox.

Got it. Did you try removing the account and then adding it back?

I'm sorry, I mean your email account on Thunderbird, on which you do not receive emails.
To delete an account, select it in the left pane of Account Settings, then Account Actions at the bottom of the left pane, Remove Account.

Ok.
Please try adding the account again.

Sure.
Do you need help resetting the password?

Ok. Keep me updated, please :)