Shift+Enter will usually enter a newline in a message without triggering send... At least that's the convention used most of the time. No guarantees on specific applications, just my own experience with this.
Some applications annoyingly use the opposite convention: Shift+Enter is what commits the entered text, while plain Enter inserts a newline.
Some applications annoyingly use the opposite convention: Shift+Enter is what commits the entered text, while plain Enter inserts a newline.