If your IP or Email provider is on the spam list only they can fix it. Your contact should be with your provider. This has nothing to do with Thunderbird.

Your answer does not make sense, because I get the following :

"An error occurred sending mail: The mail server sent an incorrect greeting: ERROR: Mail Refused - See http://www.spamhaus.org/query/bl?ip=174.107.199.81"

only if I use Outlook Express or Mozilla Thunderbird, if I go directly via the internet established by my provider everything works just fine

Your answer does not make sense, because I get the following :

"An error occurred sending mail: The mail server sent an incorrect greeting: ERROR: Mail Refused - See http://www.spamhaus.org/query/bl?ip=174.107.199.81"

only if I use Outlook Express or Mozilla Thunderbird, if I go directly via the internet established by my provider everything works just fine

Your answer does not make sense, because I get the following :

"An error occurred sending mail: The mail server sent an incorrect greeting: ERROR: Mail Refused - See http://www.spamhaus.org/query/bl?ip=174.107.199.81"

only if I use Outlook Express or Mozilla Thunderbird, if I go directly via the internet established by my provider everything works just fine

Sending via the web server and sending via the smtp server that email clients use are two completely different things. The fact that you say two different clients give the same error supports that your providers IP range or smtp server has been blacklisted. If this does not make sense to you,contact your provider and let them explain it to you. They are the ones that need to fix this.

You only need to make a response once. Duplicating it three times is unnecessary. :)

What is it that you do not understand? only if I use Outlook Express or Mozilla Thunderbird,: When you send an email it goes from your IP address via the server and on to the receiving server.

If I go directly via the internet established by my provider everything works just fine Of course it will because you are using the webmail server which is not the same.

The link will help you to find out if you are blacklisted and it provides loads of explanation and what to do. I checked the information on your behalf. It does not say that you are blacklisted as it says read the PBL FAQ's

174.107.199.81 is listed in the PBL, in the following records: PBL618016 Info given at the link: So click on the PBL FAQ

This tells me that the first thing to check is whether you are sending an email but it is not authenticated.

So check your server settings: Tools > Account Settings > Outgoing Server(SMTP) select the server name User Name should say full email address

'Authentication Method:  should say 'Normal Password'

If it does not say this click on 'Edit' select Normal Password click on OK click on OK to save changes to Account Settings.

Report back on results. If you still get a problem please post information. In thunderbird Help > Troubleshooting information click on 'Copy text to clipboard' paste info in this question.

I have done all you suggest and it did not solve the problem, of course I may have screwed something up. However I have contacted an outfit that solves such problems and they fixed it. So the issue is resolved. Thanks for trying. By the way the outfit I am referring to is PCFixSpeed, they are absolutely terrific