Send mail step in workflow

Hi experts,

For one of my workflows, in the send mail step, when we select the 'Recipient Type' as G (Organizational Object) and in 'Expression' when we pass the user ID (US ABCDE), from which table-field does the workflow pick up the e-mail ID of the user?

I believe it is not SU01 (Communication - E-mail) as there are some discrepancies over who's getting the emails and who's not in our system when I compare SU01 maintained email addresses with those who actually received the e-mails. It is not consistent with table PA0105 (InfoType 105) either.

What all things does the workflow check before sending email to the G org object users?

Thanks.