The following recipient(s) cannot be reached:
firstname.lastname@example.org on 3/4/2008 10:01 AM
The e-mail system was unable to deliver the message, but did not report a specific reason. Check the address and try again. If it still fails, contact your system administrator.
email@example.com #5.0.0 SMTP; 550 failed to meet SPF requirements
What I understand from this message is that our server doesn’t have SPF record.
SPF record is a single TXT entry in the DNS database for each domain, the main purpose of inventing this record is to fight spammers and ensure the identity of the senders.
So, how to create and test it?
By googling SPF, I found useful information; here is how to create your SPF record.
If you are hosting your own DNS server (external DNS), you can follow up in this article, otherwise, follow only step one and contact your ISP to create the record (that is if your ISP hosting your MX record).
Marc Grote wrote a good article regarding this topic, any way, here is what you have to do:
Step one: follow this wizard that will give you your SPF record, copy this string.
Step Two: go to your DNS server, under forward lookup zone, right click your (domain name) zone, and choose other new record, then select TXT record, paste your SPF record in the Text textbox. You should have something similar to this.
Now how to ensure that you create the record successfully, in other word how to query it?
This web site provide this facility, moreover you can test your SPF string before implement it.
That is it, my client start sending e-mail again and no bounce back messages.