#secure smtp server

SMTP servers are widely used to enhance emailing and boost deliverability of transactional emails. With Simple Mail Transfer Protocol servers, emailing services have become fast, easy and effective. But there are various problems related to the security of SMTP servers. If you are looking for ways to make your SMTP service secure and improve its performance then these following tips will prove to be helpful-

                                Image Source: bit.ly/1qoARP4

Manage User Access with SMTP Authentication SMTP Authentication compels the users of your server to acquire permission by providing a username and password for sending mails. This allows you to control your server and limit abuse and open relay of the server. If you are able to configure it properly, then only permitted accounts will be able to use your SMTP server to deliver emails. Limit Number of Connections It is important that you control the volume of connections to your SMTP server. You can determine the limitation through the nominal load per day and the specifications of server hardware. This is certainly one of the best ways to secure SMTP server as it is very useful in reducing DoS attacks and spam which may affect the infrastructure of your network.

Control Size of Messages Most DoS (Denial of Service) attacks tend to limit general access to a specific email server. If a particular SMTP server receives excessively large messages from an attacker, then regular outgoing and incoming mail service may get affected. As a result the attack will prove effective. However, if you restrict the size of permitted messages then it will decrease this risk significantly. When an email client will send a large message that surpasses the set limit, then he will receive an error message and the message will get delivered. The default range for messages is 1 KB to 2,048 KB. Limit Size of Single Sessions During a session, many spammers will also send innumerable messages in quick succession to your SMTP server. By sending thousands of messages, the attacker engages the server processing the messages. Thus it becomes so busy that it fails to allow the CPU cycles to respond to genuine mail requests. By controlling the total size of the session you will be able to prevent this. I would suggest that you follow the threshold which I have mentioned above. Limit Volume of Messages in Each Connection You may also safeguard your server against attackers and spammers by limiting the maximum number of messages for each connection. I would recommend that you restrict the number between 1 and 5 messages per connection as it will improve your performance. Control Volume of Permitted Recipients for Each Message Limiting the number of permitted recipients per message will help you to curb advertising mail or junk mail that is sent numerous recipients (which can reach up to 50) with just a single message. The required minimum number for SMTP RFC (number 821, in case you didn’t know) is 100. Block Spammers Using Local IP Blacklists I would suggest that you maintain a local IP blacklist as it will help you to secure SMTP server and deal with particular spammers who are targeting only your email server. Although it may take some time and effort, but this list will surely be beneficial in preventing undesirable connections from troubling your system. Activate SPF SPF or Sender Policy Framework is used to control spoofed sender addresses. Currently, most of the junk mails have a fake sender addresses. The SPF makes sure that sending MTA is sending emails from the domain name of the sender by checking its DNS Mail Exchange record. Limit Open SMTP Relay

                                Image Source: bit.ly/1lboeBJ