Primary SMTP proxy address is replaced by targetAddress value in a hybrid environment

Symptoms

Consider the following scenario:

  • In a hybrid environment, the primary SMTP proxy address of a user's mailbox is set to SMTP:FirstName.LastName@domain.com.

  • The targetAddress attribute of the user is set to SMTP:FirstName.LastName@ExternalDomain.com.

  • The email address policy in the hybrid environment is set as follows:

    • EnabledPrimarySMTPAddressTemplate: @domain.com

    • EnabledEmailAddressTemplates: {smtp:%m@domain.mail.onmicrosoft.com, SMTP:@domain.com}

In this scenario, when you run the Hybrid Configuration Wizard (HCW), the following cmdlets are run:

Set-EmailAddressPolicy -Identity "Default Policy" -ForceUpgrade "True" -EnabledEmailAddressTemplates ("SMTP: @domain.com", "smtp:%m@domain.mail.onmicrosoft.com", + "SMTP: @domain.com" + "smtp:%m@domain.mail.onmicrosoft.com")
Update-EmailAddressPolicy -Identity "Default Policy" -UpdateSecondaryAddressesOnly "True" -DomainController "GlobalCatalog.domain.com"


In this scenario, the primary SMTP address will be replaced by the value of the targetAddress attribute. The proxyAddresses attribute will now have the former primary SMTP address as a secondary address, and the attribute value will be {SMTP: FirstName.LastName@ExternalDomain.com, smtp: FirstName.LastName@domain.com, smtp: FirstName.LastName@domain.mail.onmicrosoft.com}. 

Cause

This behavior is by design, as the targetAddress attribute value is considered when you update the email address policy. 

The UpdateSecondaryAddressesOnly attribute only changes the secondary SMTP addresses. However, when the targetAddress attribute has a value, it will be added to the list of addresses of the proxyAddresses attribute. If the targetAddress is written in the form SMTP:EmailAddress, it will replace the primary address from the proxyAddresses attribute, while the former primary address (SMTP:) will now appear as a secondary address (smtp:).

Workaround

To work around this issue, user lower case instead of upper case letters for the targetAddress attribute (use smtp instead of SMTP).

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