Consider the following filter

Keep this filter (also provided in query form) in mind. We’ll come back to it later.

from: { domain1 domain2 email1 email2 }
subject: { +"exact string 1" +"exact string 2"}
CC: { email2 email3 }

OR

from: domain3 +"exact string 1"

​from: { domain1 domain2 email1 email2 } subject: { +"exact string 1" +"exact string 2"} CC: { email2 email3 } OR from: domain3 +"exact string 1"

Establishing a baseline of reliable Gmail search behavior

Before even attempting to talk about what kind of behavior to expect from an advanced filter, I want to talk about what kind of behavior you can reliably expect from Gmail search in general, when presented with a typical search query. If this seems basic or unnecessary, consider the fact that what I’m about to say is not documented by any official source.

Terms separated by spaces are joined implicitly by (AND) logical operators.

While this seemingly self evident statement is strongly suggested by the results of simple queries (such as, ​your statement is ready, for instance), it is not officially documented. It is however supported here support.google.com / … / 7190, which appears to be the sole official resource on Gmail search. Actually, by analyzing rows 4 and 14 of the official operator table provided there, my statement can be inferred logically. Let’s look at it together shall we?

• On row 4, the operator table explains that {} curly braces (which it associates with the (OR) logical operator) are used to return mail that, “matches multiple terms“.

  • It also provides the example of enclosing two (FROM) search operators (with no logical operator between) in order to filter for mail that was delivered by more than one sender.

    { from: amy from: david }
    

    ^^^ Two terms (or rather, logical operators which will evaluate to terms) enclosed in {} curly braces.

  • Since email can only have one sender, it becomes clear why the {} curly braces are associated with the (OR) logical operator in the operator table.

  • It’s because the purpose of the {} curly braces in the example is to demonstrate the idea that they should be used to return all mail from any sender representing themselves as “David” in addition to any sender representing themselves as “Amy”.

  • In other words, {} curly braces “match multiple terms“.

  • Or, terms that are separated by spaces inside of {} curly braces are joined implicitly by (OR) logical operators.

• On row 14, the operator table explains that () parentheses are used to “group multiple terms“.

  • It also provides the example of grouping two terms (with no logical operator between) for operation on by the (SUBJECT) search operator.

    subject: ( dinner movie )
    

    ^^^ Two terms grouped by () parentheses.

  • It might be tempting at this point to conclude that terms separated by spaces inside of () parentheses are joined implicitly by (AND) logical operators. But this is NOT the case. The operator table examples demonstrating the effects of () parentheses and {} curly braces are separated from each other by 8 rows for a reason.

  • To clarify, {} curly braces are described by the operator table as being useful for returning mail that “matches multiple terms“, while () parentheses are described as being useful for “grouping multiple terms” together. That’s it!

  • () parentheses do NOT impose (AND) logic on the terms (or search operators) they group. They simply group terms. That’s all they do. They are neutral in that way.

  • However (and this is important), since running this exact query results in Gmail search returning only mail that contains both terms (“dinner and “movie”) in the subject (even when subject lines that contain only one term or the other exist in the inbox), one must conclude that when this query is provided, Gmail search will only return mail with subject lines containing all parenthetically () grouped terms, which very much implies that () parentheses impose (AND) logic on the terms they group, even though they actually do not.

  • It is because of this example, the irrefutable behavior it implements, and (crucially) because of the missing example, that is,
    the one NOT shown on the operator table (Where a search operator is grouped by () parentheses):

    ( term AND search_operator: term )
    

    ^^^ Because it would be a redundant example if it were…

    That the following inexorable conclusion can be made:

Unless included terms are enclosed in {} curly braces (and regardless of whether they are grouped by () parentheses), Terms separated by spaces are joined implicitly by (AND) logical operators.

Alright… Thank you for going on that journey with me. Now that we have established a baseline for what can be considered reliable Gmail search behavior, here are a couple additional things before revisiting the filter from earlier

Expanding on the baseline of reliable Gmail search behavior

As suggested by the results of simple queries, (AND) logical operations take precedence over (OR) logical operations. This appears to hold true regardless of whether the logical operators are implemented implicitly or explicitly.

• In most of computer science there are strict rules for forming proper logical expressions. Since Gmail search provides logical operators, one would expect them to follow logical precedence. Again, this bears true for simple queries. Although, as you’ll see by the end of this question, it doesn’t take much to apparently break whatever semblance of logical precedence Gmail search imposes.

Additionally, Regardless, However or whatever… logical precedence is not suggested by any official source. And because it does take very little to seemingly break, the question is begged: If there is no logical precedence, then what is the mechanism by which Gmail search decides how to interpret your queries? How can it be exploited to achieve precision? How can I actually use it?

Lastly, simple queries suggest that search operators such as (FROM) and (SUBJECT) take precedence over logical operators.

That is to say, given the following query:

from: [email protected] AND [email protected]

Gmail search will interpret [email protected] as a term associated with the
(FROM) search operator (rather than the (AND) logical operators). To elaborate, it will return all mail (FROM) [email protected] which simultaneously contains the term [email protected] in the body.

To elaborate further, if Gmail search did NOT give precedence to search operators, then this query would result in search ignoring the (FROM) search operator, and instead returning all mail which simultaneously contains in the body the terms: [email protected] and [email protected] — regardless of what was in the (FROM) search field in the emails it returns.

Again, it is not suggested by any official sources that search operators take precedence over logical operators, but test after test after test bears this out and I defy you to show me an example where the logical operator takes precedence over the search operators.

Unfortunately without any official confirmation of these concepts though, it’s essentially impossible to understand why a filter is producing unexpected results (more on this later). But, assuming my findings from various experiments with simple queries bear out in more complex scenarios:

Here is how you would reasonably expect the filter from the top of this question to be interpreted by Gmail search:

[ f{...} AND s{...} AND c{...} ] OR [ f... AND ... ]

or simply

( f{...} s{...} c{...} ) OR [ f... AND ... ]

And for reference, the original filter:

​from: { domain1 domain2 email1 email2 } subject: { +"exact string 1" +"exact string 2"} CC: { email2 email3 } OR from: domain3 +"exact string 1"

Notice the right side of the explicit (OR) logical operator. It gets enclosed as a [] group-term. This is because:

1. The (FROM) search operator takes precedence over all logical operators.

2. The implicit (AND) logical operators positioned between the term on its right and the (FROM) search operator on its left takes precedence over the explicit (OR) logical operator.

Notice the left side of the explicit (OR) logical operator. All of it gets grouped by () parentheses. This is because:

1. According to the operator table, () parentheses are used to “group multiple terms“.

2. The implicit (AND) logical operators take precedence over the explicit (OR) logical operator.

3. Terms separated by spaces are joined implicitly by (AND) logical operators.

My question

This is NOT how Gmail search works though. And I find this to be very frustrating because:

while I would like to understand how it does work, all existing resources use simple examples to illustrate Gmail search capabilities, and fail to offer clarification on how they can be used to build more advanced queries.

And as a result of this, I can never be confident in the performance of my filters, even when they appear to be working as intended.

So yea… How does Gmail search interpret advanced queries? What is the mechanism by which Gmail search decides how to interpret your queries? And most importantly, how I can use that information to achieve precision?

I would very much appreciate any real-world-example agnostic guidance on authoring clear, readable, idiomatic queries that can be applied to any correspondence pattern with confidence that something isn’t being ignored or interpreted by Gmail search in ways that I didn’t or couldn’t expect.

Some real world examples to ponder

A couple of days ago I sent my self 15 emails containing every combination (not permutation, order doesn’t matter for this example) of the colors green, red, orange and blue. So that’s

• (green), (red), (orange), (blue)
• (green red), (green orange), (green blue), (red orange), (red blue), (orange blue)
• (green red orange) (red orange blue) (orange blue green) (blue green red)
• and finally (green red orange blue)

Then I tested Gmail search with the following two queries (which are advanced only in that I included he NOT operator):

subject: +"logical operators in Gmail search" blue red OR -blue
subject: +"logical operators in Gmail search" -blue OR blue red

By the way, to those who have found this post while seeking a way to search for an exact string, take note. according to the operator table, "" quotations can be used to search for “an exact word or phrase”, while the + operator can be used to “match a word exactly”.

• I have found that while "" quotations do seem to encourage Gmail to search a “phrase” (as in… a literal string“), it often produces fuzzy results so, rather than precise ones.

• Since this is effectively useless, I tried combining them with the + operator, which I have found works well to remove fuzzy search when matching with a single term.

• This has worked perfectly ever since I started doing it. So it seems that pairing the + operator with "" quotations results in the quoted terms being interpreted by Gmail search as a singular term.

Okay, so with the first query I thought:

“Hey this will be straight forward. The term -blue obviously filters for all mail that does NOT contain the term blue“, while the (AND) logical operator obviously takes precedence over the (OR) logical operator. So… I’ve unquestionably filtered for all mail which simultaneously contains the terms blue and red, in addition to all mail (that it hasn’t already returned) that doesn’t contain the term blue. Simple!”

This is what it returned instead:

• ( red blue )
• ( blue green red ), ( red orange blue )
• ( green red orange blue)

And that’s it. So where is all of my mail that doesn’t contain the term blue? Where is:

• ( green red orange )? Where is:
• ( red orange ), ( green orange ) and ( red green )? Where is:
• ( green ), ( red ) and ( orange )?

Gmail search didn’t think those were relevant I guess, so I tried it the other way. And I thought to myself:”

“huh… So I’m still essentially asking the same question, just in opposite order. In this query, I’ve filtered for all mail that doesn’t contain the term blue, and then I’ve also filtered for all mail that contains simultaneously the terms red and blue.”

Here is what the second query returned, instead of what I expected.

• ( red )
• ( red blue ), ( red orange ), ( green red )
• ( red orange blue ), (blue green red ), ( green red orange )
• ( green red orange blue )

Okay so, no ( orange ) and no ( green )? no ( green orange )? I mean that’s better than the last one I guess… but what happened? Also, why is it different? I mean obviously I’ve changed the order of the query, but I can’t seem to wrap my head around the Gmail search interpretation of either query I provided.

And, in the case of the first query, the only one I can think of that explains the results Gmail served up is that it just dropped the final term! Just POOF gone! Your query sucked, so I replaced it with:

subject: +"logical operators in Gmail search" red green

…

In closing

So yeah… in closing, there area number of aspects of Gmail search that are mysterious, and this translates into a lack or precision which is very frustrating.

Anyway, I’ve gone on for long enough. Please, if you need any clarification let me know. I’ll try to respond quickly.

Thanks so much in advance.