We recently getting e-mail bounce back when e-mailing certain people. It's always been fine but it started happening about 2 weeks ago.
An example of the bounce back message is:
This is the mail system at host abc.abc.abc.net.
I'm sorry to have to inform you that your message could not be delivered to one or more recipients. It's attached below.
For further assistance, please send mail to postmaster.
If you do so, please include this problem report. You can delete your own text from the attached returned message.
The mail system
<firstname.lastname@example.org>: host cluster.abc.abc.com[xxx.xxx.xxx.xxx]
said: 553 Sender Policy Framework (SPF) fail (in reply to RCPT TO command)
Any advice on how I can get this resolved?