Error: 'SMTP:contact@domain.com' is not a valid SMTP mail address (4378335)

When attempting to synchronize a new ADSContact from an Active Directory target system, the record fails to be imported by the synchronization. The logs show the following error:

[810091] Active Directory contacts: The value in Email address of object <ADSContact name> does not conform to the required format. [0] 'SMTP:contact@domain.com' is not a valid SMTP mail address. 

The mail attribute in Active Directory has 'SMTP:' in the value field, this is not a valid entry.

Please check the contents of the mail attribute for the affected contact in Active Directory Users And Computers. Confirm that the mail attribute does not have the 'SMTP:' in the value as this is incorrect. This value is only accepted in the email addresses (proxy address) attribue.