metasploit-gs/documentation/modules/auxiliary/scanner/msmail/exchange_enum.md

OWA (Outlook Webapp) is vulnerable to time-based user enumeration attacks. This module leverages all known, and even some lesser-known services exposed by default Exchange installations to enumerate email.

Error-based user enumeration for Office 365 integrated email addresses

Verification

• Start msfconsole
• use auxiliary/scanner/msmail/exchange_enum
• set (EMAILorEMAIL_FILE)
• run
• creds

Results should look something like below if valid users were found:

host      origin    service        public  private  realm  private_type
----      ------    -------        ------  -------  -----  ------------
<ip>      <ip>      443/tcp (owa)  chris@somecompany.com