Thunderbird's addressbook is not a safe sender's list, but it does ensure emails from the individual are not automatically sent to spam. Your only true safe solution for the person is to create a filter.

If you use POP and the server spam filters puts the email into the server Spam folder then you are not going to see email in a Pop mail account because pop accounts can only access and download emails that are in server Inbox. You will only see those emails if you logon to the webmail account and then locate email in Spam - mark it as not spam to put it into the server Inbox - then in Thunderbird use 'Get Messages' to download it. Please be aware that many servers auto empty Spam periodically.

Advise: logon to your webmail account via a browser and see if there is a 'safe sender' option - most server offer this, That would ensure emails from that sender stay in server Inbox. I would do this even if you use an imap account.

In Thunderbird, you can add the email address/contact to an address book then make sure the 'Junk Settings' for the account are set up correctly.

• In Account Settings
• Select 'Junk Settings' for the account.
• Suggest you enable adaptive junk controls
• select your address books to act as a whitelist - aka good email addresses.

DEstination & Retention

• Select 'Move new junk messages to'

If POP:

• select 'Junk folder on and select account'

If IMAP:

• Select: 'Other' and choose the 'Spam on account name/email address'

Note: If you use 'Imap' and email is in Junk - if it has a flame icon that is grey then server put it in Spam. If email has a red flame icon then Thunderbird put it in Spam. The Adaptive junk controls in Thunderbird need to be trained, so it's important to teach it what is junk and also what is not junk.

More info on Junk Settings: https://support.mozilla.org/en-US/kb/thunderbird-and-junk-spam-messages