You have a Microsoft Exchange Online tenant.

An external user attempts to send an email message to user$1$@contoso.com, the sender receives a non$-$delivery report $($NDR$)$ that has the following information:

$5505\mathrm{.}1\mathrm{.}10$ RESOLVER.ADR.RecipientNotFound;Recipient User$1$@Contoso.com not found by SMTP address lookup.$$

What are two possible causes of the NDR$?$ Each correct answer presents a complete solution.

Select all answers that apply.

A retention hold was placed on the mailbox of User$1.$

The email address of User$1$ is incorrect.

The email message to User$1$ has a suspicious attachment.

User$1$ does not have an active Microsoft $365$ license.