sending emails with Mail Merge is not performed through your email client (in your case Thunderbird) but directly via SMTP protocol. Hence you need to configure
Tools -> LibreOffice Writer -> Mail Merge Email and provide almost the same SMTP server settings you provided to Thunderbird configuration for sending emails. Be aware problems may occur depending on your service provider, who may refuse
- SMTP access at all —and/or
- Mass mailing (Some providers have limits of lets say x emails per y time units)
The important things here are:
- Who is you service provider?
- Does your service provider support SMTP protocol
- What is the SMTP server (servername)?
- Which Port is to be used?
- Which are the security options for your SMTP connection (is it supported by LibreOffice)
- What are the user credentials (login name and password)
If you got all the information (e.g from your Thunderbird configuration) you will be able to configure sending emails using mail merge.
Hope that helps.
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