Gmail
https://support.google.com/a/answer/2364632
To ensure that you receive emails in your inbox, you can add the email address to your contact list. If one of our mails has been moved to the spam folder, you can mark it "Not Spam" to white list it.
- Select contacts from the options on the left side of the Gmail Inbox.
- Select Create Contact on the top menu.
- Enter the email address in the primary email box.
- Select Save.
Yahoo!
https://help.yahoo.com/kb/SLN24439.html
In Yahoo Mail, your Contacts list is the best way to white list. To add the From Address to your Yahoo Contacts:
- Open your Yahoo mailbox.
- Click the address book icon at the top right of the page. When you roll your mouse over it, it will say Contacts.
- Click "Add a New Contact" at the bottom of the window.
- Fill in the fields of your Contact.
- Click Save.
Hotmail
https://support.office.com/en-us/article/block-or-allow-junk-email-settings-48c9f6f7-2309-4f95-9a4d-de987e880e46
Add the From address you want to receive mailings from to your Hotmail Safe List:
- Open your mailbox and click “Options” (upper right hand corner).
- Click the “Junk E-Mail Protection” link.
- Select the “Safe List” link.
- Copy and paste username@domain.com into the dialog box titled “Type an address or domain”.
- Click the “Add” button next to the dialog box.
If the mailing is in your "Junk E-Mail Folder", open the email and click the "Not Junk" button.
You should also check that the mailing's email address is not in your Blocked Senders list. You can find your Blocked Senders list by following the directions above and going to "Blocked Senders List" instead of "Safe List". If you see the mailing's from address on this list, select it and click the Remove button.
AOL
https://help.aol.com/articles/aol-mail-spam-and-privacy
To white list a contact in AOL:
- Click Contacts on the left navigation bar of your inbox screen.
- Then, click the New Contact icon on the top bar.
- Add the new contact information to the required fields.
- Once completed, click the Add Contact button at the bottom.
Replying to an email from a sender you want to white list will also automatically add the list as a safe sender if you're using AOL web mail.
Email from that domain will then be delivered straight to your inbox. The software will recognize that it's not spam.