Check and confirm a member of a DL received an email

Copper Contributor
Hello Microsoft Family,

We have an important member reporting another VIP member of a DL not having received an important email sent to a DL.
How do I know and where do I check, using which tool I should operate this search to 100% confirm the person received, or not at all received?

And how do I know who all received and who all not receiving the email sent to a DL?

I believe this same method of confirmation will apply to a mail sent to a Group, or Shared mailbox. If it's not, how about checking for shared-mailbox, and group?

Thank you in advance to all of you for taking your precious time to help me.

Kind regards
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