[Solution] Google 550 Authentication required

Was having issue with Google Apps email recently. The email kept on bounce back with the following error.

Delivery to the following recipient failed permanently:

email@example.sg

Technical details of permanent failure:
Google tried to deliver your message, but it was rejected by the recipient domain. We recommend contacting the other email provider for further information about the cause of this error. The error that the other server returned was: 550 550 authentication required (state 14).

Step 1 : (Basic) Check your MX record.


This is probably the basic step that most people already did. Skip if you have already setup.

• Check your MX records - http://www.mxtoolbox.com/
• Setup Google Mail records - http://www.google.com/support/a/bin/answer.py?answer=140034

Step 2 : Google SPF TXT record


For me, this help solves my problem. Although I'm not entirely sure why some of my other Google Apps email works without this TXT record.

• Check your TXT records - http://www.whatsmyip.us/txt
• Entering Google SPF record http://www.google.com/support/a/bin/answer.py?answer=178723

Note: For DirectAdmin, try "v=spf1 include:_spf.google.com ~all" (with the double-quote).

Step 1: Check your MX record.

1. You can easily check your MX record propagation at http://www.whatsmydns.net/
2. Most likely you will see different entries for some of the name servers out there.

Step 2: Flush your DNS

1. Lower TTL.
2. Delete ALL MX record entries.
3. Check your domain MX at http://www.whatsmydns.net/ again. Make sure all the name servers removed their entries.
4. Add back all Google MX records.

Hope this helps some of you out there as well. :)