From: DeskNow Knowledge Base
http://www.desknow.com/kb/

550 SPF test returned fail
http://www.desknow.com/kb/idx/11/118/article/

Someone sending you an email receives back a bounce error message saying '550 SPF test returned fail'. What does it mean?

In short, it means that the sender's mail server has misconfigured their SPF record, or that the sender is using a spoofed mail 'From' address.

SPF is an antispam measure (more details are in DeskNow administration manual, or at http://spf.pobox.com ). When DeskNow receives a message that declares it is from user@domain.com , it goes and check the SPF record for domain.com . The SPF record, if present, will list the IP address of all mail servers that are authorized to send mail from domain.com . If the message is sent to DeskNow from an IP address not listed in the SPF record, DeskNow will reject the message.

Solution

This problem could mean that the SPF record for domain.com is misconfigured . In this case the administrator of domain.com will have to correct this, otherwise any other mail server checking SPF records will reject mail from that server.

Alternatively, this could mean that the sender is sending mail using a fake 'From' address , or that he is using an SMTP server that is not authorized to send mail for that domain. He should change his SMTP settings, or his From address.

There are many web sites where you can test SPF records. Since the often change or disappear, we cannot provide a fixed address. Simply search for 'spf test' on your favourite search engine to find one.