Workers unable to submit time logs

Workers unable to submit time logs

I received a phone call and an email from employees saying that they received the same error code.
They cannot submit the hours that they worked.
The clerk whose email is problematical is not in the office this week and does not have access to her email.
She is also the email administrator.
This added topic refers to:  112382355 and the subject Fwd: Undelivered Mail Returned to Sender.
The actual error code we have received multiple times is: ERROR CODE :554 - 5.2.3 MailPolicy violation Error delivering to mailboxes