E-mail DNS SPF records

How important is a SPF record these days in reference to e-mail DNS?  We are running a SonicWall with the anti-spam filtering enabled which seems to work very well.  However, we have it set to block not just "definite spam" but also, "likely spam".  This being said, will blocking "likely spam" block e-mail that doesn't have an accurate SPF DNS record setup?
eitconsultingAsked:
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MAS (MVE)Technical Department HeadCommented:
Hi eitconsulting,
Just adding to the above. Here is a  logical diagram from Microsoft.
Mail flow.
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JohnBusiness Consultant (Owner)Commented:
An SPF record is to show people that you send email to others. It is a list of servers that are allowed to send mail and can be looked up by the receiver. It is designed to help reduce spoofing. SPF records are not for incoming mail.
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eitconsultingAuthor Commented:
The incoming e-mail messages that are being blocked by SonicWall's Anti-Spam filtering do not have valid SPF records (http://www.kitterman.com/spf/validate.html) behind their e-mail domains.
1. OURS (domain1.com)
2. VENDOR (domain2.com)
VENDOR is sending e-mail to OURS.  However, those vendors that do not have a proper SPF record (a handful of domain.coms do not reach our inboxes) established (domain2.com) are not making it past the SonicWall's anti-spam filter and into our inboxes.
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JohnBusiness Consultant (Owner)Commented:
If I understand you correctly, you (your devices) are checking the sender to find out if they are valid and they do not reply (no SPF record). You have to decide whether to whitelist or not.
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eitconsultingAuthor Commented:
It appears that our SonicWall Anti-spam filter is blocking incoming e-mail from domains that do not have valid SPF records hence, my question re: the Significance of SPF records in this day and age.
Ever since we renewed our Anti-spam filter through SonicWall, it seems to be enforcing a requirement for SPF validation and perhaps with good reason.
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JohnBusiness Consultant (Owner)Commented:
SPF records are a reasonable thing to have (my first post here) but are only one tool in the spam arsenal. They cannot be relied upon as be-all and end-all. No tool can.

So you need to figure out how to bypass or you may lose a lot of valid mail.

You cannot tell anyone to have an SPF record or tell them they must take it out.
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eitconsultingAuthor Commented:
MAS, this is helpful.  Thank you.  It seems SPF records are being enforced by the SonicWall Anti-Spam filters and perhaps for very good reasons.  However, unless everyone else complies with SPF records, SonicWall's filter is going to continue blocking the non SPF record established e-mail domains.
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