I create the newsletter with the standard template “blank”.
There is a header block as a standard part of the blank template, also inserted a text block and a footer block.
To give a better understanding I made a comparison between a mail made in the newsletter plugin and a mail with same text composed in outlook. In the link I show how the text is presented when received in outlook. As you can see the whole text block from the newsletter plugin is centered and not fully aligned to left as text from a mail made in outlook.
Yes I’m using the Text block in the composer.
In attached link I shared a screenshot of the composer with a text block and some text.
Second screenshot is how it looks in outlook, and as you can see it is not aligned to left, but text is centered.