error cannot read properties of undefined (reading 'MAILPIT') at mailpitservice.start this error is occurning in localwp

Thank you for adding to the report with you PC’s spec, @keithan. That does explain why Local can’t start Mailpit.

Mailpit does not offer a 32-bit version that Local can use. If you’re using 32-bit Windows (others can see how to check if they’re not sure), you can either upgrade to 64-bit Windows (I appreciate this is not easy and may require a new PC) or downgrade to a version of Local below 8.3.1. I’m sorry not to be able to offer an easier solution.

If you decide to downgrade from Local 8.3.1 to an older version of Local and you have existing sites, you will need to replace mailpit with mailhog in your sites.json file like this:

  1. Open the Windows File Explorer.
  2. Make sure you have enabled “show hidden items”.
  3. Browse to This PC → [your hard drive] → Users → [your username] → AppData → Roaming → Local.
  4. Make a backup of the sites.json file (it might just appear as ‘sites’) by duplicating it as sites-backup.json or similar.
  5. Open sites.json in a text editor.
  6. Find and replace ‘mailpit’ with ‘mailhog’.
  7. Find and replace ‘1.12.1’ with ‘1.0.0’.
  8. Save the file and restart Local.

You don’t need to do the above if you downgrade and have no existing sites in Local.