In which application is the attachment opened ?
It depends also on the application how the LF or CR-LF is interpreted.
There is for example a difference between Notepad and Wordpad.
Btw the Send-MailMessage cmdlet is a lot easier to use.
Try something like this
Start-Transcript-Path$Filename
...
Stop-Transcript
[string]::Join("`r`n",(Get-Content$Filename)) |Out-File$Filename
Send-MailMessage-From$EmailFrom-To$EmailTo-Subject$EmailSubject-SmtpServer$SMTPSRV-Attachments$Filename
