It is possible that your incoming settings are set up correctly however there is an error in the outgoing settings. You can find your mail settings and a step by steps guide on how to configure your email account with our Email Setup Assistant:

www.rebel.com/email/smart-setup/ 

As our outgoing mail server requires authentication, please use the same login information as your incoming mail server in order to send e-mail.

If you are still encountering issues after verifying your settings and making any necessary, there are typically three possibilities:

1. Your security settings may be so high that they are preventing your email from leaving your device. One simple test for this is to temporarily turn off or disable your security settings (i.e., firewall, anti-virus) and attempt to send an email.
2. Your IP address may appear on a blocklist. Every connection to the internet is made from a specific IP address. Some services will block email from certain IP address ranges if they have observed certain types of activity from an address in those ranges (i.e., spamming). To find out your IP address, you can visit hosting.rebel.com/myip/. To see if you appear on a blocklist, we recommend that you visit Spamhaus.org and make use of their Blocklist Removal Center. There, you can enter your IP address to see if you are on any of their blocklists. If you are on a blocklist, you will be provided with instructions on how to be removed from that blocklist.
3. Your Internet Service Provider (ISP) might actually be blocking all 3rd party outgoing mail servers. Some ISPs, such as Rogers and Telus, prefer to have more control on the data that is sent via their service, so they mandate that all emails sent while connected to them be sent via their own outgoing servers. The best way to check this is to contact your service provider and ask if they require that you use their settings for your outgoing server. If they do, they will usually provide you an outgoing server name as well as a port setting.