Solved: Thunderbird Won't Send Emails | Tech Support Guy
The Manual Method involved to fix cannot send email messages in Thunderbird are: Method 1: SMTP Settings needs to be checked. To begin, start the Thunderbird application to remove email sending problem when Thunderbird Inbox is full. After that go to Tools followed by Account Settings. Unable to send emails with Thunderbird : Support Unable to send emails with Thunderbird Modified on: Wed, 3 Feb, 2016 at 2:26 PM If you are using Thunderbird as your email client and unable to send email with VIPRE running, it is likely because the port settings in Thunderbird is not the same as those in VIPRE. Email, cannot send from Thunderbird | AT&T Community Forums
Since a power failure on Monday, I am not able to send or receive email using Mozilla Thunderbird to download from a gmail account. I was asked to validate credentials when I first tried - I entered the correct password for the gmail account but login failed.
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Unable to send emails with Thunderbird : Support
Email, cannot send from Thunderbird | AT&T Community Forums