I think so.

should I contact my internet service provider?

About what?

If about gmail authentication: The error message that you receive has a link that will lead you to the solution.

This is not your ISP’s problem, and they cannot fix it.

OK, thanks.

The image has Folder Pane and it's got only 'Local Folders' displaying, so this means you have set up a Pop account as a deferred account more commonly know as 'Global Inbox'

How to check :

• In Account Settings
• Select 'Server Settings' for pop account
• Click on 'Advanced' button

You would have this selected:

• selected: 'Inbox for different account' and 'Global Inbox (Local Folders)'
• Selected checkbox : 'Include this server when getting new mail'

If search says email is in Inbox AND you can then open it by clicking on the search result. AND threading is not enabled then it sounds like a filter of some sort is operating.

I can see from the image that 'Quick Filter' does not have any icon selected. So it does not look like the culprit.

Please check you have the following which is ideal for general use.

• View > Folders > 'All'
• View > Threads > 'All'

Now I've had a thought about replies in a specific topic with a specifc person not displaying and wonder if that is because they are set up as 'ignored'

• Please also select 'View > Threads' > 'ignored threads'

It's very easy to set up an ignore thread or subthread by using the keyboard 'K' key at wrong time. If you have inadvertantly selected an email to be ignored OR replies to an email to be ignored then it should now display and in the 'threads' column header you should see a red circle type of icon. Right click on that email and you should see the 'Ignored thread' or 'ignore subthread' option selected - so click on it to remove the setting.

See more help here on ignored threads and subthreads. https://support.mozilla.org/en-US/kb/ignore-threads

It would help to know what incoming and outgoing server settings you are using. User name in both of the following would be your full email address, so you can redact the username, but display everything else.

• Account Settings
• select name of pop account
• click on 'Edit SMTP server' button
• Post an image showing settings
• then click on OK to close
• select 'Server Settings' for pop account.
• Post image to show incoming settings

Thanks Toad Hall, In regards to your first reply,

    selected: 'Inbox for different account' and 'Global Inbox (Local Folders)'
   Selected checkbox : 'Include this server when getting new mail' 

This is how it was set, so all good there.

Please check you have the following which is ideal for general use. View > Folders > 'All' This was not checked so I checked it.

View > Threads > 'All' This I can not do because when I hover over threads all info is greyed out. I will attach screen shot

here are the server screenshots

ok, something just happened and when I went back to thunderbird just now, threads were no longer greyed out, so I clicked on all and ignored threads. Hopefully this worked!

Any idea how to fix all my emails to gmail accounts are returned to sender?

It says I am unauthenticated, but I was fine three days ago.

 grafton4@gmail.com
   host gmail-smtp-in.l.google.com [74.125.206.26]
   SMTP error from remote mail server after end of data:
   550-5.7.26 Your email has been blocked because the sender is unauthenticated.
   550-5.7.26 Gmail requires all senders to authenticate with either SPF or DKIM.
   550-5.7.26
   550-5.7.26  Authentication results:
   550-5.7.26  DKIM = did not pass
   550-5.7.26  SPF [highspeedplus.com] with ip: [192.99.139.166] = did not pass
   550-5.7.26
   550-5.7.26  For instructions on setting up authentication, go to
   550 5.7.26  https://support.google.com/mail/answer/81126#authentication

When I go to the support page they give me it has a tons of information that is all gobbledygook gook to me. I don't understand what they want me to do.

Ah, you probably do have to involve your e-mail service provider after all. I thought that you were using gmail and I misunderstood the problem.

Maybe Toad-Hall can help more.

re :View > Threads > 'All' This I can not do because when I hover over threads all info is greyed out. I will attach screen shot

You need to select a folder to see the 'Message List' and then View > Threads > 'All' will be available to choose. In the image you are viewing Account Settings, so threads would not be enabled because it's not relevant to the 'Account Settings'.

Then do the check for : Please also select 'View > Threads' > 'ignored threads'

ok, something just happened and when I went back to thunderbird just now, threads were no longer greyed out, so I clicked on all and ignored threads. Hopefully this worked!

Did you see any emails that have the ignored thread icon showing a red circle in the 'threads' column ?

re :Your email has been blocked because the sender is unauthenticated.

You have the wrong settings in your SMTP.

SMTP server settings

• DEscription: healfood
• Server Name: mail.islandnet.com

Either:

• Port: 465
• Connection SEcurity: SSL/TLS

OR

• Port: 587
• Connection SEcurity: STARTTLS

Authentication Method: Normal Password (you had select Encrypted Password which is wrong) Username: enter full email addess

re : incoming server settings- you are not using a secure method.

You need to edit the incoming server setting and get them up to date. I think your settings may have been set up a long time ago and you need to get them up to date. I have found all my information off the islandnet.com website.

• In 'Account Settings'
• Select 'Server Settings' for the pop account
• Server name: mail.islandnet.com
• Port: 995
• Username: Full email address
• Connection Security: SSL/TLS
• Authentication Method: Normal Password

After fixing the Incoming server settings and the SMTP server settings - Exit Thunderbird. Wait a few moments for all background processes to complete and then restart Thunderbird. This should ensure you are now connecting and sending securely.

Then see if you can send to a gmail email address.

Thanks for helping, Toad-Hall. Apparently, I've been wrong twice already.  :(

After making those changes, when I open thunderbird it says I cannot log in to my account.

And when I click on the get messages icon nothing happens. So now I'm not getting any mail.

I went and changed the username back to just the prefix of my email address and it's working now.

gmail not sending :(