cURL speaks SMTP natively, so you could also send to a local SMTP server, or to the SMTP server in your email provider's MX records. (For emailing myself, I've never had much trouble sending mail directly to Gmail's MX records)

    curl --mail-from "[email protected]" --mail-rcpt "[email protected]"  --ssl-reqd --url smtp://aspmx3.googlemail.com -T <(echo -e 'From: [email protected]\nTo: [email protected]\nSubject: Curl Test\n\nHello');