The indentation rules for formal letters will depend on the organization and industry.
Most industries use the full-block form, aligning everything to the left margin. It’s modern, it looks sleek and it’s easy for everyone to follow. Some employers, however, create their business letters with an indented form — and it all comes down to preference.
We highly recommend sticking to the block format if you’re unsure which one to choose. It’s universal and it looks great on paper (and email).