This help section describes the limitations of ORF.
ORF does not support filtering UUENCODED attachments. This attachment type is very rarely used in emails. UUENCODED attachments are not real attachments, they are embedded into the email parts and there is no common encoding/decoding standard for them.
The reason to ignore this kind of attachments is that filtering them would require to decode and interpret all email contents, which would be a resource-consuming process.
Although the MIME decoder in ORF supports most of the international email character sets, some charsets are not supported, for example the unicode-1-1-utf-7 character set. ORF's keyword filtering logs a warning message when a MIME body part with an unsupported character set is found in the email.
ORF treats embedded emails (MIME type message/rfc822) as monolithic parts, so the contents of these embedded emails are not checked by the content filters.
The Recipient Validation Test of ORF can validate the recipients using the Active Directory. This source looks for Microsoft® Exchange-specific AD properties and therefore it cannot work with the default Windows Active Directory which has not been extended by Microsoft® Exchange 2000-2016. This schema extension is performed by Exchange when it is installed.
On Microsoft® Exchange 2016, 2013, 2010 and 2007, the Active Directory-based Recipient Validation does not work under the Edge Transport Server role. Other recipient sources work and the Hub Transport Server role is also supported.
Under the Edge Transport Server role, Microsoft uses a different Active Directory server (ADAM) and LDAP structure.
If only the Client Access Server (CAS) role is available on the Exchange 2013 server ORF is installed to, the Routing Agent and the Inbound Signing Agent will not be installed, so the Auto Sender Whitelist and ARC Signing features, and On Arrival filtering will not be available. Due to this, the only possible action upon blacklisting is rejection, and the emails will not be signed. If only the Mailbox role is available, the SMTP Receive Agent will not be installed, thus Before Arrival filtering will not be available.
As a workaround, install ORF on the Edge Transport Server role. Alternatively, you can install ORF on the CAS and Mailbox roles and keep their configuration in sync using the Configuration Synchronization feature. Either workaround will make the full feature available.
To learn more about Exchange 2013 deployment scenarios and limitations, please read our related Knowledge Base article.