Microsoft office.com/setup program is the ideal package for computing tasks, use by multinational companies and personal users all over the globe. There are issues related to security settings that create email delivery problems in the office 365 edition. You can read about the steps given here for fixing the error 5.7.1.

Removing The Restrictions For The Sender

  • You can change the settings in group for unblocking the sender; And add the sender to the list that includes the allowed senders. You will require creating a mail user or contact for representing the external sender in the organization.
  • The sender appears to be restricte as they are external or outside of your organization. you can configure the settings in the group for accepting the messages from the outside senders. In case a mail flow rule has been configured, which s otherwise called transport rule for restricting the group of senders, you can easily alter the rule for the messages via the sender to be accepted.

If You Are The Email Admin

  • You can fix the issues of email delivery by configuring the public folder for accepting the external sender’s messages. For this, you can open the center of exchange admin. When the EAC opens, you can navigate to the public folders and then choose the public folder that appears in the list.
  • After this, click on the edit option. Now in the properties of the public folder dialog box, you can navigate to the settings of mail flow. you can configure the settings that appear in the mail flow dialog box. These settings will allow you to accept the messages from the senders.
  • Start by un-ticking the checkbox that states require that the users are authenticate. After this, choose the option of all senders. When done with these steps, you can click the save tab.

When you have completed these steps, you can check if the issue of email delivery has been successfully resolved in the www.office.com/setup 365 edition.

Source - https://www.offiice-officecom.com/blog/methods-for-fixing-the-error-code-5-7-1-for-email-delivery-issues-in-office-365-edition/