When you run the IdFix DirSync Error Remediation Tool in your on-premises Active Directory Domain Services (AD DS) environment, "format" is displayed in the ERROR column for one or more objects.
This issue occurs if the email address of the object is not a valid, publicly routed email address.
To resolve this issue, specify the correct email address of the object. To do this, follow these steps:
In the UPDATE column for the object, type the email address of the object.
In the ACTION column, click EDIT, and then click Apply.
Repeat steps 1 and 2 for each object that has a "format" entry in the ERROR column.
Run IdFix again to look for more object errors.
IdFix first checks the mail attribute of an object. If the attribute is blank, IdFix then checks the user principal name (UPN). The tool uses DNS to check whether the email address can resolve to an MX record. If neither the mail attribute nor the UPN contains a valid email address, "format" is returned in the ERROR column.
Note Make sure that the email address contains only valid characters. For more information, see the "Directory object preparation" sections of the following Microsoft website:
Microsoft Azure cloud services, Microsoft Azure Active Directory, Microsoft Office 365, Microsoft Intune, CRM Online via Office 365 E Plans, Microsoft Azure Recovery Services, Office 365 Identity Management