Invoice email not being received

Version 20.2.65 (I think)
Over the last 2 days, when I’m sending invoice emails to clients, they are not receiving them. I’m getting the copy to my email address ok.
All 3 clients are using hotmail. The fact that I’m getting the copies (non-hotmail), suggests hotmail might have started rejecting them but I don’t know?
Anyone else having issues? Any idea of a fix?

These circumstances prove it is a Hotmail issue. The email copy you are receiving is sent exactly the same way. Hotmail may be interpreting you as a spammer. Ask your clients to check their junk mail. If your mails are not there, they will need to inquire with Hotmail.