smtp.comcast.net not accepting email from MFD scan to email
I am a Tech Service Provider in Oregon. It has been a local practice for many years for many local providers of MFD devices (Copier/Scanners etc.) to set up scan to email using an outgoing SMTP server of smtp.comcast.net via port 25 and no authentication for scan to email functionality from these devices. Up until very recently this has always worked without fail for businesses that are connected using a Comcast Business Internet data circuit. It has been my understanding that for Comcast Business Internet subscribers that port 25 was not blocked and that smtp.comcast.net could be used for outgoing email from a MFP device in this manner.
Beginning in August 2021, Within the last couple of weeks, I've received trouble calls from a large number of clients stating that scan to email is no longer working. In every case, the client is a Comcast Business Internet customer and their MFD was set up to use smtp.comcast.net via port 25 with no authentication. In many cases I was able to switch the outgoing SMTP server to Microsoft Office 365 using a O365 receive connector if the client has a Static IP from Comcast. For other clients without a static IP any possible resolution was a bit more complicated.
My question comes in a couple of parts.
What changed on smtp.comcast.net to cause this to fail. Are there alternate settings that should be used to allow scan to email to work from these MFD copier/scanner devices if they still wish or need to use smtp.comcast.net as their outgoing SMTP server?
These are all Comcast Business Internet data circuit customers. I understand that things are different for Xfinity home users where for those users port 25 was blocked and they required a secure connection and authentication.