Notes room reservation does not work from O365. The resource mapping is properly set.
O365 forwarding address: 365.domainname.com
Notes internet address: domainname.com
1.- Access the "Address Rewriting" section under Mail connector on the CMN console.
2.- Enable checkbox "Rewrite Notes Addresses.
3.- Add DomainName.com.
4.- Select checkbox "Rewrite RCPT TO (Recipients) Commands".
Note: If there are other O365 objects which forwarding address is also different, for instance External.DomainName.com, then add this domain name before DomainName.com. CMN will find the first match and then exit.
If WORKAROUND1 does not fix the issue, please check if the Notes address lookup is set to fullname only, if that is the case the Domino server will never accept an inbound SMTP message for a global domain alias.
If there is a dedicated Domino server that can be used for CMN > Domino inbound connection you should set this SMTP configuration to fullname and local part, and specify the CMN mail connector IP in the inbound relay list for security. Otherwise, set CMN MC to translate the inbound SMTP address back to the primary, and configure the resource mapping as required (no sub domain).