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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

dgibbs
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2 Answers2

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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.

MadHatter
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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
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    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
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    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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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 neutral status — the domain owner is not offering an opinion about whether the message should pass.

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

Andy Swift
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David W
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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
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    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 03:19
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    I dont know who to upvote so I'm upvoting you all – Brock Hensley Mar 05 '14 at 03:40