Sunday, October 9, 2016
When you send email from your server, your email can be recognised by client name as un-secure/un-trustable if you use a third party provided domain name.
This is pretty normal, as any body can send email with the form they likes and it will be delivered.
For exemple I can send email in the form "email@example.com", but most email Client while detect this email as suspicious due to the fact my IP sending the email may not have the right on the domain "ubuntu.com".
To evaluate emails rights, Client will ask the domain name owner if IP sending the email is allowed to use this email name, this information is contained in TXT records of a DNS as SPF value.