Mail Delivery methods are a powerful element in the Jetpack CRM arsenal of tools. Occasionally a specific host/server provider has curious settings that need tweaking for Jetpack CRM Mail Delivery to work with their setup. Here’s some things to try if you are using Rackspace shared hosting:
Allowing Plain-text
A common point seems to be that this setting on Rackspace server setup stops Jetpack CRM Mail sending out: “Allow Plaintext”. Try this first, by enabling this setting:

Firewall
Try turning it on and off again!
- Disable the firewall
- Restart the firewall
Port check
Please see this guide re: opening ports on rackspace, (you may or may not need to do this step).