Exchange turns off basic SMTP in December and its own alternative keeps it until 2028
At the end of December, Exchange Online stops accepting a username and password to send mail by default. The date has already moved three times and the final one has not even been announced; what does not change is that the rejection is permanent, is not queued and warns nobody. We walk through the timeline with Microsoft's own wording, why its official escape hatch still accepts passwords until September 2028, the five alternatives and their small print, and the switches to check in your tenant before it lands.
Microsoft 365
ES 
CAT 
EN