Emails sent to internal email accounts work. Emails to external email accounts fail.
Not being able to send to external mail clients is NOT due to a setting within our software. While we do have a hidden/optional configuration setting should a customer request this, it is not done by default, and is not the source of this issue.
Speak with your IT/mail administrators and tell them "your mail server is blocking sending/relay to external emails". This is happening at your mail server, not within our software. They will either open the server/set something for you to be able to do this or they may give you a different port to use or security setting to configure within our software.