Gmail Search – Does It Only Recognize Whole Words?

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I've lots of emails in my spam with the title "Undelivered Mail Returned to Sender"(My site was hacked and is sending out trash mails that got bounced back to my Gmail).

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While I was trying to inspect these spams I noticed this behavior of Gmail search that I was never aware of:

If I search "undelivered" then all the emails with this subject will be brought up:

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But if I search only part of the word like "undeliver" or "undeliv" there will not be any results:

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Is this intended? When I try to search in Gmail should I always search the whole word instead of only part of it?

Best Answer

When in Inbox or All Mail, search picks up partial words as well (as you can see in the uploaded image).

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But. Not when it comes to Bin, Spam or any label or category for that matter.

In general: Unless searched before, fragmented/nested searches using Search Operators will not pick/suggest any partial words.
That means searches like: is:, in:, label:, from:, to: and so on.