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Is there any difference between

v=spf1 +a +mx -all

and

v=spf1 a mx -all

I am unsure if they do the same thing or somthing different. Clarification would be great. Thank you

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2 Answers

up vote -1 down vote accepted

Technically, yes, there is a difference. According to the SPF Record Syntax, a plus sign (+) indicates that the record should pass, no questions asked. The absence of a plus sign, or the inclusion of a question mark (?) indicates a "neutral" status - i.e. the domain owner is not saying 1 way or another whether that particular record should pass.

However, the end result is (almost) always the same: The email will pass.

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The default identifier is + so they have the same outcome, just the intent is more obvious when using the first notation. I guess someone could override the default interpretation by their SPF setup (whoever manages the server receiving mails), but it seems unlikely. –  dunxd Apr 16 '13 at 12:12
4  
From the page you reference: The default qualifier is "+", so no qualifier is the same as "+". It is not the same as a "?", and nowhere on that page is something like that mentioned. If SPF on the whole can't come up with a match then a "neutral" result is returned, but that's not the same as a mechanism qualifier. –  Chris S Apr 16 '13 at 13:40
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Good grief... Yes, you're right. But if you look further down, it says this: "Mechanisms are evaluated in order. If no mechanism or modifier matches, the default result is 'Neutral'." I give up trying to be helpful on serverfault (not really, but this is frustrating). –  David W Apr 16 '13 at 13:53
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DavidW, I think that I see your point. I stipulate that you've given an excellent and accurate answer to the question "What happens if I have a completely blank SPF record, or it contains only mechanisms that cannot ever match?", and I have to admit, I've wondered about that myself - and now will wonder no more. Sadly, the OP didn't ask that question. –  MadHatter Apr 16 '13 at 15:53
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I'll upvote that. :) –  David W Apr 17 '13 at 3:19
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The SPF record syntax summary, right at the top, states that

If a mechanism results in a hit, its qualifier value is used. The default qualifier is "+", i.e. "Pass".

So it seems clear to me that there's no technical difference between mx and +mx.

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Well, I think we're talking semantics. I see a slight difference, but I'm a stickler for grammar and clarification. =) In reality, there's no difference at all (or at least shouldn't be), unless a receiving mail server admin has a misconfigured server. –  David W Apr 16 '13 at 12:26
    
David, it's not a semantic issue. You said that "The absence of a plus sign, or the inclusion of a question mark (?) indicates a "neutral" status". The first half of that is simply wrong; the standard is clear that absence of any sign indicates a plus sign. –  MadHatter Apr 16 '13 at 12:28
    
Thanks everyone for your answers. It has clarified that the difference is so small that is doesn't really matter which one you put. However I have decided to add the + to the records as the plus mean pass. –  dgibbs Apr 17 '13 at 10:49
    
As does no plus - that's the point of my answer. There is no difference, DavidW's misunderstanding notwithstanding. –  MadHatter May 19 '13 at 16:37
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