The American Heritage Dictionary has this usage note:
When used in occupational terms like waitress, stewardess, and sculptress, the feminine suffix -ess is sometimes considered sexist and demeaning because it gratuitously calls attention to gender. With some nouns, like poetess or sculptress, the feminine form may be taken to imply that the task somehow differs when performed by a woman, or that it is by default the realm of men. With others, such as seamstress, the feminine form may be taken to suggest the occupation is characteristically feminine. In some cases, such as sculptor, the term with masculine gender has become effectively neuter, applying naturally to either sex. In other cases, gender-neutral terms like server and flight attendant have been created, finessing the problem of using an originally masculine noun to refer to either sex. A few specialized examples persist in fields in which the sex of the referent is relevant, sometimes for historical reasons, including chiefess in anthropology, goddess in history and literature, and lioness in biology. Other cases, like webmistress, represent arch reclaimings of the -ess suffix, but these are whimsical or ironic exceptions. · Many nouns ending in -or or -er are commonly used of women now and should be considered standard. In our 1997 survey, 95 percent of the Usage Panel approved The gallery is exhibiting work of sculptor Barbara Hepworth, and in our 2016 survey, 88 percent accepted Meryl Streep was one of five actors to receive an Oscar nomination for leading woman this year. It should be noted that 85 percent of the panelists also accepted a similar sentence with actresses, indicating that in some cases, despite the prevalence of gender-neutral terms like actor, the -ess form maintains its acceptability. However, when discussing mixed-sex groups, actors is preferred over actors and actresses: Ninety-three percent of the panelists accepted Meryl Streep was one of four actors presented with honorary doctorates yesterday, together with Robert Duvall, Helen Mirren, and Javier Bardem, whereas only 67 percent accepted a similar sentence with actors and actresses in place of actors.