Hotmail to Google Apps 550 Authentication Error Solution

Hotmail to Google Apps 550 Authentication Error Solution


Since moving our emails to Google Apps, we've always had intermittent issues with receiving emails from Hotmail, Live and Outlook email addresses. Google Apps is a fantastic tool with loads of additional features, but it's no good if you can't receive emails from their rivals over at Microsoft.

After spending hours over the past months researching and trying to find a fix for the horrid 550 authentication error which at the time I believed to be with a setting in Google Apps, I finally found a solution to it. Microsoft, unlike any other email provider,' use your domain names A records to send mail to, not the MX record specified at the registrar. This is fine If the mail server is on the same server as your web server'.

If it isn't you are most definitely in for a fun ride and hours of painstaking problem solving. Thankfully we found a solution and we will get to that soon.

The Google Apps Gmail and Hotmail 550 authentication issues are easily rectified if you have a dedicated server with no other hosted websites. You simply block SMTP port 25 and hey presto! Problem solved. Sadly if you have a VPS where you host other clients emails & websites then you can't block that port as they won't receive emails.

After finally speaking to the team at Google - who were also baffled (email attached) I decided to carry on problem solving. In the end, I discovered a 100% effective way to overcome the Google Apps not receiving emails from Hotmail by blocking the IP addresses that Microsoft use to send their emails. This boycotts them sending them to the web servers A records and then uses the MX records they should be using all along!

If using Linux and Cpanel you can directly block Hotmail IP addresses in the console, sadly this didn't work for me. Upon testing, I was still getting bounced emails in Hotmail with the error 550 authentication. Frustrated, I went to bed thinking that there must be a way to rectify this problem.

At 3 am, my usual awakening time for troubleshooting, I woke with the brain wave... A CDN - that's what we need! If I can't use the servers firewall, I can set the website up using a Content Delivery Network (Cloudflare Free plan) and use their firewall to block Microsoft's IPs sending mail to the A records. This will then re-route the emails to the Google Apps MX records!

The next morning that's what I tried... low and behold, SUCCESS! We finally overcame the issue of not receiving Hotmail emails to my Google Apps Business account! This was a painstaking process that we had been looking into on and off for months but finally found a resolution for VPS owners. So much so that the guys over at Google are going to document the solution going forward for any other clients who happen to have this issue and looking online there's quite a few. A simple fix in the end but took hours of tinkering until something just clicked.

For more info on solving the dreaded 550 Authentication error contact us.