This is a bug report.
In the ‘New Message’ window, pressing the [Tab] key in the Subject field moves the focus to the body, but it also inserts a tab character.
Additionally, when I press the [Delete] key on an attachment, character ‘’ (U+007F) is inserted at the beginning of the message body.
This happens to me as well. Tabbing from subject line to move into the main body, adds a tab in the beginning of the body text.
Happened on MacOS 15.7.x Sequoia and Tahoe 26.3.1
eM Client version: 10.4.4867 (a1d5549) in an English (US) environment.