ssmtp

You can use Twilio SendGrid as the SMTP relay for ssmtp, a lightweight mail transfer agent for Unix-like systems. To add SendGrid as an SMTP relay for ssmtp, edit /etc/ssmtp/ssmtp.conf and add the following:

1
mailhub=smtp.sendgrid.net:587
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AuthUser=apikey
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AuthPass=sendgridapikey
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UseSTARTTLS=YES

Your changes will come into effect as soon as the next message is sent via ssmtp.