Wrapper function to simplify generating a mail message for Send-MgUserMail with Microsoft Graph

New-MgMailMessage.ps1

#Requires -Modules Microsoft.Graph.Authentication, Microsoft.Graph.Users.Actions
function New-MgMailMessage {
    param (
        [Parameter(Mandatory=$true)]
        [string]$Subject,
        [Parameter(Mandatory=$true)]
        [string]$Body,
        [Parameter(Mandatory=$false)]
        [ValidateSet("Text", "Html")]
        [string]$BodyType = "Text",
        [Parameter(Mandatory=$true)]
        [string[]]$To,
        [Parameter(Mandatory=$false)]
        [string[]]$Cc,
        [Parameter(Mandatory=$false)]
        [string[]]$Bcc,
        [Parameter(Mandatory=$false)]
        [string[]]$Attachments,
        [Parameter(Mandatory=$false)]
        [ValidateSet("High", "Low")]
        [string[]]$Importance,
        [Parameter(Mandatory=$false)]
        [string[]]$ReplyTo
    )

    $Message = @{}
    $Message.Subject = $Subject
    If ($Importance)
    {
        $Message.Importance = "$Importance"
    }
    $Message.Body = @{
        ContentType = $BodyType
        Content = $Body
    }
    $Message.ToRecipients = @()
    foreach ($Address in $To)
    {
        $Message.ToRecipients += @{
            EmailAddress = @{
                Address = $Address
            }
        }
    }
    If ($Cc)
    {
        $Message.CcRecipients = @()
        foreach ($Address in $Cc)
        {
            $Message.CcRecipients += @{
                EmailAddress = @{
                    Address = $Address
                }
            }
        }
    }
    If ($Bcc)
    {
        $Message.BccRecipients = @()
        foreach ($Address in $Bcc)
        {
            $Message.BccRecipients += @{
                EmailAddress = @{
                    Address = $Address
                }
            }
        }
    }
    If ($Attachments)
    {
        $Message.Attachments = @()
        foreach ($Attachment in $Attachments)
        {
            $attachementBytes = [System.Convert]::ToBase64String([System.IO.File]::ReadAllBytes($Attachment))
            $attachmentName = Split-Path -Path $Attachment -Leaf -ErrorAction Stop
            $Message.Attachments += @{
                "@odata.type" = "#microsoft.graph.fileAttachment"
				Name = $attachmentName
				ContentBytes = $attachementBytes
            }
        }
    }   
    If ($ReplyTo)
    {
        $Message.ReplyTo = @()
        foreach ($Address in $ReplyTo)
        {
            $Message.ReplyTo += @{
                EmailAddress = @{
                    Address = $Address
                }
            }
        }
    }
    return $Message
}

##############
## Examples ##
##############

# Simple message
$Message = New-MgMailMessage -Subject "Hi there" -Body "How ya doin?" -To "bill.gates@contoso.com" 

# Message with Bcc, attachments, importance and reply to
$Message = New-MgMailMessage -Subject "Hi there" -Body "How ya doin?" -To "bill.gates@contoso.com" -Bcc "satya.nadella@contoso.com" -Attachments "C:\Users\me\Downloads\0023970129-1.PDF","C:\Temp\MyCSVfile.csv" -Importance High -ReplyTo "noreply@contoso.com"

# Html message
$html = Get-Process | Select -Property Name,Id,Path | ConvertTo-Html -PreContent "<h2>Running processes on my system</h2>" | Out-String
$Message = New-MgMailMessage -Subject "Running processes" -Body $html -BodyType Html -To "bill.gates@contoso.com"

# Send the message
Connect-MgGraph -Scopes Mail.Send
$Result = Send-MgUserMail -UserId 'sender@contoso.com' -Message $Message -SaveToSentItems -PassThru