Our Internal email attachments are blocked by F-Secure filter even if strip attachment rule is deact

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Customer_Care Posts: 548 F-Secure Employee


Strip attachments for internal emails are being filter by F-Secure Email and Server Security, though the strip attachments option is turned off.


Th email direction is based on the Internal Domains and Internal SMTP senders settings and it is determined as follows:

  1. Email messages are considered internal if they come from internal SMTP sender hosts and mail recipients belong to one of the specified internal domains (internal recipients).
  2. Email messages are considered outgoing if they come from internal SMTP sender hosts and mail recipients do not belong to the specified internal domains (external recipients).
  3. Email messages that come from hosts that are not defined as internal SMTP sender hosts are considered incoming.
  4.  Email messages submitted via MAPI or Pickup Folder are treated as if they are sent from the internal SMTP sender host.
Note: If email messages come from internal SMTP sender hosts and contain both internal and external recipients, messages are split and processed as internal and outgoing respectively.

Internal Domains

Specify internal domains. Messages coming to internal domains are considered to be inbound mail unless they come from internal SMTP sender hosts. Internal Domains Separate each domain name with a space. You can use an asterisk (*) as a wildcard. For example, *example.com internal.example.net

Internal SMTP Senders

Specify the IP addresses of hosts that belong to your organization. Specify all hosts within the organization that Internal SMTP Senders send messages to Exchange Edge or Hub servers via SMTP as Internal SMTP Senders. Separate each IP address with a space. An IP address range can be defined as:
• a network/netmask pair (for example,,
Note: There is also virus scanning, where mb infections are blocked
• a network/nnn CIDR specification (for example,, or
• IPv6 address (for example, 1::, 2001::765d 2001::0-5, 2001:db8:abcd:0012::0/64, 2001:db8:abcd:abcd::/52, ::1).
You can use an asterisk (*)to match any number or dash (-) to define a range of numbers. For example, 172.16.*.1 172.16.250-255.*
Note: If end-users in the organization use other than Microsoft Outlook email client to send and receive email, it is recommended to specify all end-user workstations as Internal SMTP Senders.
Note: If the organization has Exchange Edge and Hub servers,the server with the Hub role installed should be added to the Internal SMTP Sender on the server where the Edge role is installed.
Important: Do not specify the server where the Edge role is installed as Internal SMTP Sender.

You can make these changes on the Web GUI. To do so, open F-Secure Email and Server Security Web Console and navigate  to settings.
  1. Open the Administration from menu and navigate to Network
  2. Expend the Network section and enter the list of the Internal domains as explained above
  3. Enter the Internal SMTP senders as explained above
Note: Network internal domains and internal smtp senders - determine email direction (inbound, outbound, internal) and then apply corresponding filters

Article no: 000018032