Causes of Email Prefixes for Users in Azure AD Tenant

Question

Causes of Email Prefixes for Users in Azure AD Tenant

Chaitanya Kulkarni 0

The application utilizes Azure AD for identity validation, and token received from Azure AD is used to populate user properties within the application after login. It has been observed that some users invited to the tenant have a mail# prefix added to their login email in the 'Other Emails' property, while the primary Email property is occasionally left blank. This results in the prefix being returned when fetching the email in the application. What factors contribute to this behavior, and how can the addition of this prefix be prevented for new users created in the tenant?

Carolyne 1,151 Reputation points Microsoft Employee

2026-02-02T15:24:39.8533333+00:00

Hello Chaitanya!
Typically this happens for B2B guest users invited via email, especially when they authenticate using email one‑time passcode (OTP) or don’t have an existing Azure AD / Microsoft account; Entra stores the external email as an identity of type mail, which surfaces as mail# in OtherEmails while the primary Mail attribute can remain empty

Your answer

Carolyne 1,151 Reputation points Microsoft Employee

2026-02-02T15:24:39.8533333+00:00

Hello Chaitanya!
Typically this happens for B2B guest users invited via email, especially when they authenticate using email one‑time passcode (OTP) or don’t have an existing Azure AD / Microsoft account; Entra stores the external email as an identity of type mail, which surfaces as mail# in OtherEmails while the primary Mail attribute can remain empty