If your Thunderbird or Outlook client stopped working with Verizon email accounts, then this may be why.

• You can no longer use:
  incoming.verizon.net (incoming Pop server)
  outgoing.verizon.net (outgoing SMTP server)
• You must now use:
  pop.verizon.net (incoming Pop server)
  smtp.verizon.net (outgoing SMTP server)

Here is the article from Verizon Support:

Please Note: Verizon has recently updated our email client settings to improve security. Please review the settings below to verify that your email software client (e.g. Outlook, Outlook Express, etc.) has the most recent configuration.

Before you begin:
You’ll need the following email settings:
Incoming mail server (POP3): pop.verizon.net
Incoming Server Port Numbers: 995
Outgoing mail server (SMTP): smtp.verizon.net
Outgoing Server Port Numbers: 465 Why is this important?
Make sure SSL encryption is enabled for the incoming and outgoing mail server.
For more email and remote access configuration options see Verizon Online Email Settings

P.S.  If you are using Avast Antivirus (which will scan encrypted email messages), then after you change your server names in Thunderbird, you will need to confirm a security exception for POP and SMTP server names in Thunderbird (for the avast scanner proxies to work properly) and also at some point re-enter your valid password and check the box to save and manage your password with the Thunderbird password manager.