SMTP Client

An SMTP client that utilizes smtp2go as a email relay server

Table of Contents

1. Description
2. Program Output
3. Compile and Execute
4. Function Headers
5. Structures
6. Other

Description

Simple Mail Transport Protocol (SMTP) is an email protocol used to send email messages. This C based email client uses a TCP socket to connect to smtp2go.

Users can enter:

• Sender's name and email address
• Recipient's name and email address
• Email subject
• Email message

One email can be sent with each execution of this program.

NOTE: You will need to make an account with smtp2go prior to using this program.

Once an account is made, add a SMTP User via the settings tab.

The username and password, used to create the user, will be the credentials you will use with the program.

Program Output

NOTE:

All information above is used for demonstration purposes only (i.e. not real credentials)

Compile and Execute

• Windows:

  To compile run the command gcc main.c headers.c -o email_client

  To execute run the command email_client.exe

• Linux / Mac

  To compile run the command gcc main.c headers.c -o email_client

  To execute run the command ./email_client

Function Headers

struct Account_info get_account_info(char smtp_server[], int smtp_port)

• Description:

  Get the smtp2go username and password from user

• Parameters:

  char smtp_server[] Represents hostname of smtp2go

  int smtp_port Represents port number used to connect to smtp2go

• Return:

  struct Account_info Struct containing username and password of smtp2go account

---

int connect_to_server(char smtp_server[], int smtp_port)

• Description:

  Makes connection to the smtp2go server

• Parameters:

  char smtp_server[] Represents the hostname of smtp2go

  int smtp_port Represents the port number to connect to smtp2go

• Return:

  int Represents the file descriptor of the TCP socket made when connecting

---

char *base64_encode(char* data)

• Description:

  Base 64 encoding the sting passed to it Special thanks to this user for providing the details of this function: source

• Parameters:

  char* data Represents the string to be encoded

• Return:

  char* Represents base64 encoded string

---

void authenticate_account(int sock_fd, char* encoded_username, char* encoded_password)

• Description:

  Authenticates username and password with the smtp2go server

• Parameters:

  int sock_fd TCP socket file descriptor used to connect to server

  char* encoded_username Base64 encoded username

  char* encoded_password Base64 encoded password

• Return:

  None

---

struct Email_info get_email_details()

• Description:

  Gets all information required to send email

• Parameters:

  None

• Return:

  struct Email_info Contains senders name and email address, recipients name and email address, email subject, and email body

---

struct Email_commands format_commands(struct Email_info info)

• Description:

  Formats commands to send to the smtp2go server for email transmission

• Parameters:

  struct Email_info info Struct containing details of the email given by user

• Return:

  struct Email_commands Struct containing commands to be sent to the smtp2go server

---

void send_commands(int sock_fd, struct Email_commands commands)

• Description:

  Writes commands to the smtp2go server and checks for successful acknowledgements from the server

• Parameters:

  int sock_fd TCP socket file descriptor used to connect to server

  struct Email_commands commands Struct containing commands to send to server

• Return:

  None

---

void close_connection(int sock_fd)

• Description:

  Closes TCP socket to smtp2go

• Parameters:

  int sock_fd TCP socket file descriptor used to connect to server

• Return:

  None

Structures

struct Account_info

• Description:

  Holds username and password for smtp2go account

• Variables:

  char username[_1BYTE] Username for smtp2go account

  char password[_1KB] Password associated with username for smtp2go account

---

struct Email_info

• Description:

  Holds information needed to send email

• Variables:

  char senders_name[EMAIL_SIZE] Name of whos sending the email

  char recipients_name[EMAIL_SIZE] Name of whos recieving the email

  char source[EMAIL_SIZE] Email address of sender

  char destination[EMAIL_SIZE] Email address of recipients

  char subject[SUBJECT_SIZE] Emails subject

  char body[BODY_SIZE]] Emails body

---

struct Email_commands

• Description:

  Holds commands to be sent to smtp2go for sending email

• Variables:

  char from_email[_1BYTE] Tells server the source email address

  char to_email[_1BYTE] Tells server the destination email address

  char data[_1BYTE] Tells server that email data is being sent next

  char from_name[_1BYTE] Tells server the name of the person whos sending the email

  char to_name[_1BYTE] Tells server the name of the person whos receiving the email

  char subject[_1BYTE] Tells server the subject of the email

  char body[BODY_SIZE] Tells server the body of the email

Other

EMAIL_SIZE 30 Max number of characters for senders name and email address, recipients name and email address

SUBJECT_SIZE 50 Max number of characters for the subject of email

BODY_SIZE 10000 Max number of characters for the body of email