There are multiple reasons that eventually led Thunderbird not sending emails. Therefore, to fix that the best ways are:
- Export Thunderbird data in MBOX, create a new Thunderbird profile, and import clean data using the MailsWare Thunderbird Converter.
- Check and fix the internet connection.
- Reduce the size of email attachments.
- Repair the outbox folder.
- Check and do the required settings of SMTP.
- Launch Thunderbird in safe mode.
For more details, read the blog linked above and make your Thunderbird usage process easier than ever before.
