Email provider, software, addon to stop work server filtering EVERYthing

1st, not sure if this is best forum to post this question - don't know what a solution may involve (if there is one).

Last couple mos, spouse's work email server started filtering nearly ANY msgs I send. In past yrs, never a prob. We don't send msgs daily or dozens / day. It's generally if need to get msg to spouse at work that won't wait. Spouse's msgs out often get filtered, like: "Meeting after work - be home late." Or, "Please call doctor & make appt." Some teachers complaining msgs from parents getting filtered.

No doubt something's changed w/ school's software & having probs, but still need to find way around this issue. Usually nothing in msgs that would trigger "normal" spam filters. Might be like, "Dr office called - call nurse 555- 555-5555." If happened in just a few, I could understand. Tried changing my mail server - same prob. Tried sending msgs to spouse's private mail acct (not school's email acct) - filtered that, too.

Because spouse can't get phone calls during work & may not hear (or have time to respond) to text msgs, need other ideas to try & see if can get * at least * important msgs past their server.

Spouse can't "legally" install software on school issued laptop. I could get past (probably have to change) admin PW to allow installing say, encryption software, etc., but COULD get in trouble if they find out. Think most mail providers w/ some kind of encryption require installing some software to use service?

Any ideas of other ways - using some particular mail provider, etc., that could help? In general, their server doesn't like many types of attachments. In past, most attachments got filtered, if not whole msg, even for PDF, DOC. Never tried attaching a simple txt doc - but assume server could / would scan as well. Spouse doesn't have / can't install any encryption software, so that seems unavailable.

Thanks for suggestions.