$Body = "<i>Enter your HTML Waffle here</i>"
$Creds = Get-Credential

$MailProps = @{
    To = "Joe.Bloggs@domain.com"
    From = "Joe.Bloggs@domain2.com"
    Body = $Body
    BodyAsHTML = $true

    Subject = "Test"
    UseSSL = $true
    Port = 587
    SMTPServer = "smtp.domain.com"
    Credential = $Creds
    Attachments = "C:\temp\file.txt"
}

Send-Mail @MailProps