Enabling Bounce Notifications (NDR's) at Rackspace
If you are using Rackspace as your incoming (MX) email server, and you wish to receive a bounce notification (NDR) whenever an email that you send via SMTP2GO bounces, you may need to ask them to whitelist SMTP2GO's IP addresses. This is because, as per SMTP protocol, we send bounce notifications from a blank sender email address, which Rackspace blocks by default.
If you have a dedicated IP address with us, you can simply ask them to whitelist that particular IP address.
If you don't have a dedicated IP address, you'll need to ask them to whitelist our ranges of IP addresses, which can be found by looking at the SPF record for spf.smtp2go.com: