Printing envelopes
alignment of return address on the envelope
iMac 21.5", macOS 10.14
The return address on Pages v8 supplied templates is a text box. Each line of text within that text box is placeholder text, that you can single-click, and type over with your specific information. The text box is not locked, so alignment on the envelope, or text alignment within the text box is straight forward.
Be more detailed in your post requirements.