Scan to Email Fails Despite Successful "Save and Test" from HP Smart

[HindsightIs2040]

HP Scan to Email, whereby you can scan a document and send it do any targeted email -- a feature available only from the control panel on the 8710 -- has simply stopped working and cannot be repaired.

All other functions on the printer work -- printing, scanning to my own computer (both control panel and PC), Scan to network folder (control panel), checking status/ink levels/IP address and connectivity, and so on -- and even an uncountable number of successful "save and test" runs of the "scan to email" setup window inside HP Smart, during which a test email is successfully relayed to the targeted email I provide using the credentials specified.  However, when when I attempt to scan from the printer to a targeted email address moments later, it fails with one of two errors 

1) A cryptic "Network error" (I can still see the printer, show status, print IP address, print to it, check ink levels, and scan from computer while this failure message is displayed on the control panel),    

2) Invalid login credentials. 

My suspicion is that the new single-app security feature added to SMTP servers like **bleep** and ATT (i have an att.net email), which prevent routine connection to an SMTP server unless a dedicated password is provided for the application, is "eating" the password and preventing the printer from connecting to the network and sending the scan after the test.  I have set up these single-app passwords for both outlook on my PC and for the printer, and have tested the credentials from HP smart.  The scan works fine up until the file is to be sent, when the failure appears. 

I have:

Uninstalled and reinstalled HP Smart 

Reinstalled and reconfigured the printer 

Ceated multiple (maybe 20) single-app passwords and used them to "save and test" the scan to email feature from HP smart, and received "success" emails from the test in my outlook inbox. 

"Saved" the configuration without using the HP Smart test feature, and then tried to scan from the printer (which then provides the 'invalid credentials' error).

Validated that the SMTP configuration is correct because I am receiving outlook emails after using HP smart to do the "save and test" config

No one in my family can scan and send an email to their own account. My pc has to be in the house and I have to scan for them, which is completely impractical. 

Has this feature been killed by this new "so called" SMTP security feature?  Is there a solution that someone has found out there?  Nothing in the forum addresses this.  AT&T says it is an HP printer problem, but i can successfully send an email from the printer if I use HP smart to do a test, but otherwise cannot. 

[Echo_Lake]

@HindsightIs2040

Thank you for posting on HP Support Community.

Don't worry as I'll be glad to help, 
I understand scan to email stopped working, it looks like the gatekeeper on mac is blocking the scanning software, follow steps on - https://support.apple.com/en-us/HT202491

Is there any antivirus software installed on your Mac?
 

Hope this helps! Keep me posted for further assistance.
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