Sporadic issues with Access using Outlook to send email via a scheduled task

We have some coding inside of Microsoft Access where we pull data out of a database, create a .pdf and then send to users using Outlook.  This works most of the time but probably once a week, the email is generated with the report and then it won't send (we get an undeliverable error):

Your message did not reach some or all of the intended recipients.

      Subject:      Daily Lab Reports for 6/24/2019
      Sent:      6/25/2019 9:12 AM

The following recipient(s) cannot be reached:

      QC Database Email Group on 6/25/2019 9:12 AM
            This message could not be sent. The client operation failed. Try sending the message again later, or contact your network administrator.


Diagnostic information for administrators:

Error is [0x80004005-0x000004b9-0x00000501].
Submit-Message failed: message id(1), failure enum(6), HResult(0x80004005), EC(0).

This doesn't tell me much so I have no idea why it works most of the time but fails sometimes...

I have no issues sending emails using Outlook (manually) but it just seems to be problematic when something else is kicking off opening Outlook and sending the email.  I did turn off the "never warn me about suspicious activity" in the trust center - otherwise, we get the popup every time the task would run to "allow" another application to send email.
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John TsioumprisSoftware & Systems EngineerCommented:
Do you have an anti virus (especially Norton Antivirus)...can you test if by disabling it gets the job done ?
vianceadminAuthor Commented:
Sorry, I should have said that initially.  We have Webroot and I had turned that off temporarily - still had issues even thought it was disabled.
John TsioumprisSoftware & Systems EngineerCommented:
Well the info you get is not much use...it might be a system issue or a network issue....or an application issue .
Nevertheless using Outlook automation to send emails means that you add another layer of possible issues given the fact that Outlook is much more than a simple email client ...so maybe even as a test you could try to use a more Access based solution for sending emails.
Two are the main free solutions
1. vbSendMail
2. CDO ..there are some mentions that it has issues with Exchange...till 2007 that i used it..after a bit of configuration i was working fine but i don't know about later versions
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