A couple of DNS zones were deleted by accident and restored pretty quickly. However now all of those domains are bouncing emails with the following message.
The response from the remote server was: 550 Please turn on SMTP Authentication in your mail client. mail-lj1-f178.google.com [188.8.131.52]:45603 is not permitted to relay through this server without authentication. Reporting-MTA: dns; googlemail.com Arrival-Date: Mon, 21 Jan 2019 14:12:53 -0800 (PST) X-Original-Message-ID: <redacted> Final-Recipient: rfc822; [email protected] Action: failed Status: 5.0.0 Remote-MTA: dns; mx1.domain.tld (IP redacted, the server for the domain redacted.tld.) Diagnostic-Code: smtp; 550-Please turn on SMTP Authentication in your mail client. 550-mail-lj1-f178.google.com [184.108.40.206]:45603 is not permitted to relay 550 through this server without authentication. Last-Attempt-Date: Mon, 21 Jan 2019 14:13:44 -0800 (PST)