Show email address instead of primary field

Hi,

I have a custom entity, which uses an auto number as its primary field.

Now we have enabled emailing to that entity. The emails sent to this record is showing the auto number as the recipient name in outlook. I know the system will take the primary field as the recipient name but, as per the current design, it is not possible to change the auto number to another field. Is it possible to prevent the system from taking the primary field as recipient name?

Thanks,

Nijo