Awesome, adding "| Out-String" was the ticket. It's nothing fancy obviously but here's the complete script. It's handy for me so it might be handy for someone else. Thanks a million for the help Clinton, this will save me a solid 45-60 minutes per day. If you're ever in the Cincinnati area let me know, I owe you a few beers.
# Provide controller hostnames, IP's or FQDN's. Add/remove additional as needed.
$filer1 = "xxx"
$filer2 = "xxx"
$filer3 = "xxx"
$filer4 = "xxx"
# Recipient e-mail address
$recipient = "xxx@somewhere"
# Sender e-mail address
$sender = "xxx@somewhere"
# Your SMTP server
$smtpserver = "mailserver"
$vols = $null
$line = "
"
Clear
Connect-NaController $filer1
$vols += Get-NaVol | Out-String
$vols += $line
Connect-NaController $filer2
$vols += Get-NaVol | Out-String
$vols += $line
Connect-NaController $filer3
$vols += Get-NaVol | Out-String
$vols += $line
Connect-NaController $filer4
$vols += Get-NaVol | Out-String
Send-MailMessage -to $recipient -From $sender -Subject "Volume Report" -SmtpServer $smtpserver -Body "$vols"