Enabling Open option for Forms to open in outlook for SharePoint

1.
 Login to the server -> inetmgr(IIS) -> Click on the server name -> On right side select MIME types -> Double click on it and then Click on Add.
File name extension: .oft
MIME type: application/vnd.ms-outlook

2. Run the following below Powershell script on the SharePoint Management Shell.

$webApp = Get-SPWebApplication "http://webapplication name"
If ($webApp.AllowedInlineDownloadedMimeTypes -notcontains "application/vnd.ms-outlook")
{
  $webApp.AllowedInlineDownloadedMimeTypes.Add("application/vnd.ms-outlook")
  $webApp.Update()
  Write-Host "application/vnd.ms-outlook added to AllowedInlineDownloadedMimeTypes"
  }