Description:
Unable to send an email via Mail Merge, it would be ideal if I could have an option to delegate the email transmission aspects to my Mail Transfer Agent (MTA) which in this case is Thunderbird.

Steps to Reproduce:
0. Write up a mail merge "file" with an associated contact database.
1. Click on "Send Mail Messages"
2. Select "To: Email Address"
3. If desired, enter a subject line.
4. Select "Send as: Plain Text"
5. Click on "Send Documents"

Actual Results:
A redacted error log is included below.

<class 'smtplib.SMTPSenderRefused'>: (550, b'5.7.1 Authentication is required to use this service', 'EMAIL'), traceback follows
  File "C:\Program Files\LibreOffice\program\mailmerge.py", line 262, in sendMailMessage
    self.server.sendmail(sendermail, truerecipients, msg.as_string())
  File "C:\Program Files\LibreOffice\program\python-core-3.8.16\lib\smtplib.py", line 885, in sendmail
    raise SMTPSenderRefused(code, resp, from_addr)

Expected Results:
Email is sent


Reproducible: Always


User Profile Reset: No

Additional Info:
Additional Info:
Version: 7.5.4.2 (X86_64) / LibreOffice Community
Build ID: 36ccfdc35048b057fd9854c757a8b67ec53977b6
CPU threads: 16; OS: Windows 10.0 Build 19045; UI render: Skia/Raster; VCL: win
Locale: en-NZ (en_NZ); UI: en-US
Calc: CL threaded

Tools -> Options -> Libre Office Writer -> Mail Merge Email -> Test Settings (screenshot will be attached.)