Tegamibachi, Violet Evergarden Recommendations
Letter Bee and Violet Evergarden are beautiful stories about delivering meaningful letters. Both feature an alternative world where the protagonist is not entirely human and is entitled to deliver those very special letters to different clients. The settings seem to be European-inspired, vintage style, with a hint of sci-fi, as Experiments (Tegami Bachi) and Dolls (Violet Evergarden) are made. Also to mention that the protagonist lost someone very dear to him/her and that lead to his/her current path.
Both are slice-of-life with a little bit of adventure/action and amazing artwork, so if you liked one, you'll probably enjoy the other.