Security when Sending Email Introduction Ulysses (user) - sends emails and attachments using private key cryptography to send them from LAN to LAN. From the user's perspective, email seems so simple. Select the address of the person you want to send the email to, compose the message and click "Send". All done Actually, sending your message into the cloud is a bit like sending Little Red Riding Hood deep into the dark woods. You never know what could happen. Ulysses sends an email and an image which is classified as an attachment to the email, when sending the email the user uses private key encryption to send the email to another user. A private key is used to generate digital signatures and to decrypt data. Also can be used for authentication, data encryption/decryption, digital signature and secure email. Message sending process? Once the user sends the email, here's how it progresses to the end user?. Your Internet service provider has a special computer called a mail server, which is responsible for collecting mail from its customers. When you click the send button, your computer connects to the mail server and transmits the message along with the recipient list. The message is transmitted with Simple Mail Transfer Protocol (SMTP). SMTP is a language used by your mail program to communicate with the mail server. SMTP allows your email program to specify the recipient list and message text. The recipient of your destination also has an Internet service provider. They also have a mail server. When your SMTP server decides it's time to send your email, it connects to the destination mail server and passes the message to it. They use SMTP to talk to each other. Therefore the destination mail server is often called Destination SMTP Server. When the recipient decides to check the email, his email program connects to the destination SMTP server and retrieves the mail from the server. This time they use Post Office Protocol Version 3 (POP3), which is a language used to receive mail. Therefore, this server is usually called Inbound POP3 Server. - Messages are sent via TCP port 25. Receive message and decrypt Once the user receives the mail, only the valid user can view the message. Additionally, to make sure the message is legitimate and tell who it is from using the digital signature, the end user will use the public key to decrypt the message. The user opens his email program and receives the mail, his email program sends a request via Internet connection to the Pop3 server (via TCP port 110) and downloads the message to his computer where he sees the sender's message.