Funny thing happend……
For some reason new email accounts (older then 24 hours) and email aliases was not working properly within Office365.
External contacts was reporting:
tried to deliver your message, but it was rejected by the server for the recipient domain mydomain by mydomain.mail.protection.outlook.com
550 5.4.1 [<username>@<mydomain>]: Recipient address rejected: Access denied
Reason:
- Accounts was is getting propagated in an accepted time frame (24 hours)
Issue:
- Â The affected accounts is unable to receive email from external contacts – emails are not getting delivered.
Resolution:
- We changed the accepted domain to Internal relay to resolve the issue.
- As a precaution we enabled Conditional Sender ID and NDR backscatter to avoid spam attacks.
Articles on Mail Flow for reference:
Exchange Online Protection Limits
https://technet.microsoft.com/en-in/library/exchange-online-protection-limits.aspx
How Office 365 does SPF checks for customer-to-customer mail
http://blogs.msdn.com/b/tzink/archive/2015/02/26/how-office-365-does-spf-checks-for-customer-to-customer-mail.aspx
Manage Transport Rules
http://technet.microsoft.com/en-us/library/jj657505(v=exchg.150).aspx
Transport rules
https://technet.microsoft.com/en-IN/library/jj919238(v=exchg.150).aspx
Configure your spam filter policies
http://technet.microsoft.com/en-us/library/jj200684(v=exchg.150).aspx
Submitting spam and non-spam messages to Microsoft for analysis
http://technet.microsoft.com/en-IN/library/jj200769(v=exchg.150).aspx
Advanced spam filtering options
http://technet.microsoft.com/en-us/library/jj200750(v=exchg.150).aspx
Spam email and Office 365 environment
http://blogs.technet.com/b/exchange/archive/2014/07/25/spam-email-and-office-365-environment-overview.aspx