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Cannot send email. What version of Thunderbird is present? What kind of security program is installed?

There is not a lot of information. Can you describe this situation a little bit more then that?

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Verify that the SMTP setting for the outgoing mail is correct, that the SMTP server is oke. Other things could block this sending service. Had you have a update lately on the pc? Could be that Thunderbird is not trusted after these updates ,now but the previous version still is or does.you can delete Thunderbird from the list of trusted software and place it back. Ports can being blocked by using old numbers for them in or for the SMTP setting area of the outgoing service for it. Try to use a different portnumber ,the other port number should be 587 instead of the 25 number for the outgoing port service .

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If you somehow found out it is the SMTP password that is bugging you and it has to change,then you can try to solve that issue. Use the Reset email password form ,where? Change this subject on the isp support site.

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