It is recommended to send emails in multipart format. This means that both the text and HTML versions of the email are sent. The recipient's email software automatically determines which version to display. In most cases, the HTML format is used to display emails.

It is also possible to send only the text version of an email. However, this version cannot include formatting such as colors or size definitions. If only the HTML version is sent, there is a risk that spam filters may mistakenly classify the message as spam. Many spam filters check the ratio between text and source code in an email. Sending in multipart format, which includes an additional text version, improves this ratio and reduces the likelihood that the email will be caught in a spam filter.

To change or check the format of your emails, open the desired mailing and navigate to Advanced Settings > Type and Format > Format.