That's ging to be tricky, but you can perhaps figure it out.
If I send an email that looks like that.
"Why don’t you call me"
Then the Vault result come back as this. Not the same.

And if I instead send an email with a proper sentence.
"Why don't you call me"
the result comes back a this, a different code than what you were looking for.

This different code also seems to be the one used by Outlook Online, as I sent a test email from there.

However, that HTML reference, 't, can't be used by itself, at all.
It matches nothing in Vault, maybe because it searches the real text, even if the preview only shows semi-broken HTML. Opening the individual email in Vault shows only the proper text, and no HTML.
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https://wheretofind.me/@NoSubstitute