Administrator's Guide - Kerio Software Archive

Chapter 15 Sending and Receiving MailHide local IP in Received headersKerio MailServer will hide the local IP address (included in the IP address group definedin the Relay Control tab of Configuration → SMTP server) in the Received part of themessage header.Each SMTP server that the message passes through inserts an entry into this field, specifyingwhere the message came from, where it is going and who received it. This impliesthat the first record in the Received header contains the sender’s email and IP addresses.If the SMTP server is placed on a private network behind a firewall, the client’s privateIP address is inserted. This means that outgoing email messages can carry informationabout a private network that would normally be hidden from the Internet. This informationcould make it easier for a potential hacker to attack such networks. Only switch thisoption on if Kerio MailServer is installed on a private network behind a firewall (even if itruns on the same machine as the firewall).There is a connection to relay control here so that the mailserver recognizes local IP addresses.In relay control, a group of local IP addresses is usually used to define addressesfrom which mail can be sent to any domain (see chapter 15.2).Note: If relay control is disabled or no local IP address group is defined, this option willhave no effect.Insert X-Envelope-To header...Defines if the X-Envelope-To entry will be inserted into the header of messages deliveredlocally. X-Envelope-To is the original recipient address based on the SMTP envelope.This option is useful especially if there is a domain mailbox in Kerio MailServer.Enable decoding of TNEF messagesTNEF (Transport Neutral Encapsulation Format) is a Microsoft’s, proprietary format usedto send messages with format extensions from MS Outlook. The winmail.dat file isattached to any message sent in this format. It contains a complete copy of the messagein RTF along with all attachments. This implies that if a user does not access their emailvia MS Outlook and an email message with an attachment in this format will be deliveredto their mailbox, the attachment cannot be opened.The TNEF decoder built-in Kerio MailServer decodes TNEF messages at the server’s sidein the standard MIME format and helps avoid winmail.dat attachment difficulties.Use this option if users do not access their email only by MS Outlook.Note: If any problems regarding message decoding occur, the Debug log may help whereit is necessary to enable the Message decoding option. See chapter 22.8 for more information.Enable conversion of uuencoded messages to MIMEUuencode (Unix-to-Unix Encoding) is an encoding method used for sending of files byemail. It encodes binary data to a text format so that the data can be inserted directly tomessage bodies. The main problem is that some email clients may miss a special decoderwhich decodes the encoded files and transforms them to their original format. Therefore,Kerio MailServer includes a built-in Uudecode decoder (Unix-to-Unix decoding). Emailmessages are decoded to the standard MIME format on the server’s side so that users do158