Is it inappropriate to tell my students to check their school email? I am a new STEM faculty member at a primarily undergraduate institution. I emailed my students (through the school-mandated online course management system) before the beginning of the term about the availability of the syllabus online, as well as other things. Several students told me that they hadn't checked their emails and didn't know where to find the syllabus. I have also sent emails to students about their testing accommodations, only to learn that the students hadn't read my email to them even though it concerned an upcoming quiz.

Would it be inappropriate for me to make a general announcement in class that it is important for students to check their school email accounts frequently, as that is how I plan on communicating with them? I certainly won't call out any students or mention any specific scenarios that prompted this announcement.
At every (US) institution I've attended or worked at, there's been an official school-wide policy that students are expected to check their school email regularly, and that sending official communications there constitutes sufficient notification.  So check your school's policies; if you have such a policy, then it's certainly appropriate to remind students about it.

Moreover, in such a case, you can enforce it: if you send an email to school accounts saying "Please respond by date X if you want Y", and they don't respond by date X (whether because they didn't check their email or for any other reason), you may not be under any obligation to give them Y.  (Disability accommodations could have special rules so contact your school's disability office to check on that.)