The main purpose of this thesis is to describe the whole development process of the Spamler application. The main goal of the application is to generate email traffic for training and testing tasks in JYVSECTEC company. Spamler should send emails for multiple recipients with HTML or plain text template. The HTML template can also contain embedded images, which must be inserted into emails as attachment.

Described is the whole process from the beginning, the collecting and writing of the requirements through designing the database and then creating the main API, and the thesis finishes with the explanation of the created web-based client.

The backend of the service was developed in Go programming language designed by Google, as REST API. All emails are sent in goroutines, which is equivalent to threads in other programming languages. The persistent storage is implemented with the SQLite database system and the configuration of the application is saved in the configuration file in the TOML format.

Users can manipulate the service only via this API using JSON format for data transfers. For better user experience, a client is created as web page in HTML, CSS and JavaScript communication with the created API.