Do you have a pop or imap mail account ?

Have you logged onto your webmail account using a browser to see if emails are in server 'Inbox' or 'spam' folders ? If they have not arrived on server then Thunderbird cannot see them.

Confirm email has been received and can be seen in the webmail account.

If you use POP and the webmail account shows the email in 'Spam', then Thunderbird cannot download it as POP can only have access to the Inbox. So move it back to webmail Inbox and then in Thunderbird, click on 'get Messages' to download it.

Various ways of getting to see 'Account Settings.

Via 'Menu bar': 'Tools' > 'Account Settings' > 'Junk Settings' for mail account

Via 'Mail Toolbar': 'Menu icon' > 'Options' > 'Account Settings' > 'Junk Settings' for mail account

Via 'Folder Pane': Right click on mail account and select 'Settings' then select 'Junk Settings' for the mail account.

When setting up 'Junk Controls' you can select address books to act as 'whitelist', but this really only effects how Junk controls deal with emails that have already been downloaded.

• http://kb.mozillazine.org/Junk_Mail_Controls
• https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages

see image below as a guide

Do you have a pop or imap mail account ? It is an IMAP account.

No, the emails are not appearing in the server in box or junk mail folders.

I have updated and changed email addresses, and I get no emails from Twitter despite clicking resend a number of times.

I have reviewed and checked all the set up for junk mail on T-bird. All appears to be correct.

Interestingly, when I delete an email from gmail, it's gone. It does not appear in the trash folder, as do other emails from my other email accounts where the deleted email tracks to the trash folder. Yet, the setting for the gmail account is for deleted emails to go to the trash folder. They don't.

I wonder if the two issues are related?