Gmail:

Mark messages as ‘Not spam’

If Gmail has marked emails you wish to whitelist as spam, tell Gmail the emails are not spam.

  1. In Gmail, navigate to the spam folder.
  2. Search for emails containing the domain you wish to whitelist (eg onlinegroups.net).
  3. Select all the emails shown.
  4. Click More and then Not spam.

Source: http://onlinegroups.net/blog/2014/02/25/how-to-whitelist-an-email-address/

Hotmail:

  1. Sign in to your account. Go to inbox.
  2. Click

Options located at the upper-right side of the page.

  1. Select

More Options.

  1. Under

Preventing junk email, click Safe and blocked senders.

  1. Click

Safe Senders.

  1. In the text box, type in the email address or domain you’d like to always receive email from, and then click

Add to list >>.

Source: https://answers.microsoft.com/en-us/outlook_com/forum/oemail-osend/e-mail-domain-name-whitelisting-for-hotmail-users/65cf50f8-65a1-4128-81d7-3d2e8f4bbbd6

Yahoo:

  1. Navigate to "Settings" icon, then click "More Settings" from the Yahoo Mail menu.
  2. Select "Filters" and hit "Add" to enter information about the domain name or sender.
  3. From here, you can enter any string of text you want to whitelist in future emails.

Source: https://clean.email/how-to-whitelist-an-email

Outlook:

  1. Go to the Home tab.
  2. In the Delete group, select Junk.
  3. Select Junk E-mail Options.
  4. In the Junk Email Options dialog box, go to the Safe Senders tab.
  5. Select Add.
  6. In the Add address or domain dialog box, enter the email address or domain name you want to safelist. For example, janedoe@example.com or @example.com.
  7. Select OK.
  8. The email address or domain appears in the Safe Senders List.
  9. Select OK.

Source: https://www.lifewire.com/add-address-domain-safe-senders-outlook-1173760

AOL:

  1. From Aol Mail, select Contacts
  2. Select the New Contact icon
  3. Enter the contact’s information, especially the email address of the sender in the Email 1 field
  4. Select Add Contact

Unmark email as spam:

  1. Go to Aol Mail on your computer’s web browser
  2. Select the Spam folder
  3. Open the desired email
  4. Select the Not Spam (OK) icon at the top of the page. The email will return to your Inbox.

Source: https://www.whitelist.guide/aol/

BTinternet:

To make sure that emails you wish to receive are never put into your Spam, you can add them as a “Safe Sender”.

  1. From the Settings tab, select the Safe senders" folder and click on the Add button
  2. Add the email address you want to mark as safe and click Save
  3. After a confirmation message the email address will be added to your list of safe senders
  4. To remove a safe sender you just need to click on the Delete button

Source: https://www.bt.com/help/email/using-bt-mail-s-anti-spam-features

Virgin Media:

  1. Sign in to Virgin Media at mail.virginmedia.com
  2. Click the System menu icon on the top right of the screen
  3. Click the Settings menu
  4. Expand the Email option
  5. Select SPAM Settings
  6. Select the required SPAM setting:
    • Reject All SPAM messages
    • Move message to Spam folder (default)
    • Flag a message as SPAM but deliver to Inbox
    • Turn off all SPAM filtering
  7. Navigate away from the SPAM Settings page – this will save the chosen setting

Marking an email as SPAM or NOT SPAM in Virgin Media Mail will move that email to the relevant folder, but doesn't maintain that choice for future messages for that sender.

If emails from a particular sender are being identified incorrectly as SPAM, save the sender as a contact. This will ensure you receive all messages from that sender and their messages won’t be identified as SPAM. For more information on how to add a contact, check Using the Address Book in Virgin Media Mail.

Source: https://www.virginmedia.com/help/virgin-media-mail-email-spam-settings

Fastmail:

Update your contacts:

Emails that come from senders in your contact list get special treatment. They avoid greylisting and get a reduced spam score. If you use an email client, you don't have to enter addresses into your Fastmail contact list manually. You can upload contacts in different formats on the Settings → Import & Setup screen.

You can also add entire domains to your contact list. This will ensure that mail sent from any address at this domain is not marked as spam. You can add a contact with the email address *@domain.tld to your contact list in the Email field. Entries in a shared contact group are also included.

If you don't want to clutter up your contacts with lots of domains (for example: legitimate mailing lists), create a single contact called Whitelist and add each domain to that entry as extra addresses in the Email field.

Source: https://www.fastmail.com/help/receive/stopspam.html#whitelist