Function to allow advanced table styling in HTML based emails opened in Outlook

Convertto-OutlookHTMLTable.ps1

Function Convertto-OutlookHTMLTable {
    Param(
        [Parameter(ParameterSetName='CSVInput')]
        [string]$CSVFile,
        [Parameter(ParameterSetName='CSVInput')]
        [string]$Delimiter = ',',
        [Parameter(ParameterSetName='InputObject')]
        [object]$InputObject,
        [string]$CSS,
        [string]$CSSFile
    )

    #region CSSSetup
    
    if ($CSS) {
        $csssplit = $Css -split '\n|\r' | ?{$_}
    } elseif ($CSSFile){
        $csssplit = Get-Content $CSSFile | ?{$_}
    } else {
        Write-Error -Message 'No CSS Specified' -ErrorAction Stop
    }

    # Since css/html in outlook is bad (https://msdn.microsoft.com/en-us/library/aa338201(v=office.12).aspx)
    # The below code takes the css for col(n) and "tbody tr:nth-child(odd/even)" and tries to combine them
    # The priority is col > tr

    
    If($csssplit -contains "tbody tr:nth-child(odd) {"){
        $i = 0
        $s = 0
        $e = 0
        $csssplit | ForEach-Object{
            $i++
            If($_.Trim() -eq "tbody tr:nth-child(odd) {"){
                $s = $i
            }
            If(($e -lt $s) -and ($_.Trim() -eq "}")){
                $e = $i-2
            }
        }
        $oddstyle = "style=`"" + ($csssplit[$s..$e] -join '') + '"'
    }
    If($csssplit -contains "tbody tr:nth-child(even) {"){
        $i = 0
        $s = 0
        $e = 0
        $csssplit | ForEach-Object{
            $i++
            If($_.Trim() -eq "tbody tr:nth-child(even) {"){
                $s = $i
            }
            If(($e -lt $s) -and ($_.Trim() -eq "}")){
                $e = $i-2
            }
        }
        $evenstyle = "style=`"" + ($csssplit[$s..$e] -join '') + '"'
    }

    #endregion CSSSetup

    #region CSVSetup

    if ($PSCmdlet.ParameterSetName -eq 'CSVInput'){
        $InputObject = Import-Csv $CSVFile -Delimiter $Delimiter

    }

    $Columns = $InputObject[0].PSObject.Properties.Name

    #Generate Column CSS (as col1, col2, col3 etc)
    $colgroups = 1..($Columns.Count) | ForEach-Object{"<col class=`"col$_`" />"}
    $colgroup = "<colgroup>$colgroups</colgroup>"

    #Create table headers
    $tableheaders = $Columns | ForEach-Object{"<th>$_</th>"}
    $thead = "<thead><tr>$tableheaders</tr></thead>"

    #endregion CSVSetup
                
    #region BuildRows
    $i = 0
    $tablerows = $InputObject | ForEach-Object {
        $i++
        $c = 0
        $ThisFormattedRow = $_.psobject.properties | ForEach-Object{
            $c++
            $ci = 0
            $s = 0
            $e = 0
            $font = $null
            $style = $null

            If($csssplit -contains ".col$c {"){
                $csssplit | ForEach-Object{
                    $ci++
                    If($_.Trim() -eq ".col$c {"){
                        $s = $ci
                    }
                    If(($e -lt $s) -and ($_.Trim() -eq "}")){
                        $e = $ci-2
                    }
                }
                $csssplit[$s..$e] | ForEach-Object{
                    If($_.Trim().Startswith("color:")){
                        $font = $_.Trim().replace(';','')
                        $font = $font.Split(':')[0].trim()+"=`""+$font.Split(':')[1].trim()+"`""
                    }
                    Else{$style+=$_.Trim()}
                } 
                If($null -ne $font){
                    $fstyle = "<font $font>"
                }
                $cstyle = "style=`"$style`""
            }
            if($null -ne $font){$t = "$fstyle$($_.value)</font></td>"}
            else{$t = "$($_.value)</td>"}
            If($null -ne $style){$s = "<td $cstyle>"}
            else{$s = "<td>"}
            "$s$t"
        }
                    
                    
        If($i%2 -eq 1) {
            "<tr $evenstyle>$ThisFormattedRow</tr>"
        } else {
            "<tr $oddstyle>$ThisFormattedRow</tr>"
        }
    }
    #endregion BuildRows

    $tbody = "<tbody>$tablerows</tbody>"
                
    $table = -join('<table>',$colgroup,$thead,$tbody,'</table>')
    Return $table
    
}

Based on code found here