You are sending mail through Exclaimer Cloud back to Office 365 using connectors, you may experience issues such as –
- 550 5.0.350 Remote server returned an error -> 553 Message filtered. Refer to the Troubleshooting page at;http://www.symanteccloud.com/troubleshooting for more;information. (#5.7.1)
- Headers too large (32768 max)
There is a known issue within the Microsoft Office 365 infrastructure which means that a subset of Exchange Online servers are not correctly stripping the “X-MS-Exchange-Diagnostic-Untrusted” headers from the message.
This results in bloated headers which upstream providers are not able to process and thus the email gets rejected.
There is a bug raised within the Microsoft engineering team to resolve this issue. The Microsoft SHD number for this is EX107354.
Update as of 28/6/17: The coding is in place within Microsoft to resolve this and is being tested now. We are told the fix for this will be deployed as part of a new build however the deployment process can take some time in an infrastructure as large and complex as Office 365.
There is a work around for this issue in the short term until Microsoft deploy their permanent fix.
Please create a new transport rule in your Office 365 tenancy as below. Note, some of these settings are only available after you click “More options…” in the new rule window–