Administrator's Guide - Kerio Software Archive

Chapter 15 Sending and Receiving MailMessage size limitSetting of maximum message size can be used for the following purposes:• to limit size of attachments sent to Kerio WebMail by an HTTP POST request,• to set maximum size of memory allocated in Kerio MailServer to each HTTP POSTrequest.Warning: Maximal value of the limit is 128 MB. It is not possible to enter a greater valuein the Kerio Administration Console.For better understanding of the limit, here is an explanation of how a message writtenin Kerio WebMail is sent to Kerio MailServer. Each new message composed in the webinterface is sent by a browser via HTTP protocol using an HTTP POST request to KerioWebMail. The interface receives the message and processes it so that Kerio MailServercan send it to the addressee by SMTP protocol.Each HTTP POST request contains one message including a message body, all headersand attachments. The limit set by this option narrows size of any HTTP POST requestdirected to Kerio WebMail. This means that any limit set for requests also limits size ofemail messages.Size limit set for HTTP POST requests is applied to any files sent from Kerio WebMailto Kerio MailServer and it is applied to all Kerio MailServer users. The default valuefor maximum size of messages sent from Kerio WebMail is 20 MB. This limit should begenerally satisfactory for these purposes.The minimum value for the limit is 2 MB. If any lower limit is entered in the Maximumsize of messages that can be sent entry, the 2 MB value is set automatically.If a message includes any attachments, they are encrypted by the Base64 method. Thistype of encoding is able to increase the size of transmitted data even by one third (in caseof binary data). This means that, for example, the minimum 2 MB limit might also allowjust 1 — 1,5 MB attachments.It is necessary that a memory allocation value is specified in Kerio MailServer for HTTPPOST requests. The more bulky the request is the more memory must be allocated. Thisimplies that the size of the allocated memory changes according to changes in the sizelimit.Warning: Any time the limit is changed, it is necessary to restart Kerio MailServer sincethe memory allocation is changed as well.Session securitySession security depends on methods and manners how users manage connection toKerio WebMail. Users often simply close their browsers without logging out of KerioWebMail. In such cases, the session is not interrupted and it can be misused more easily(the session is the more risky the longer it takes). For this reason, it is possible to setsession timeout. If the user does not use the session over the timeout, connection to theserver is interrupted automatically when this timeout runs out. By default, the timeout isset for one hour.Maximum time can also be set for sessions in addition to the session’s expiration time.The maximum session time means the time since user’s connection. If users use the168