That seems like it would be discriminatory, because the message contains no sex or gender-specific language, and sending the same message to the women would tak

That seems like it would be discriminatory, because the message contains no sex or gender-specific language, and sending the same message to the women would take no more time (per employee) than the men. Modifying the message to contain gender-specific language would mean that the manager would have to have two templates, but intentionally creating a gender-specific template for the purpose of excluding one group would itself be discriminatory.