Using MS-Outlook on an iMac 27" 2020, macOS Big Sur 11.3.1, Norton Deluxe 360, some emails with attachments won't send. They sit in the outbox and error messages indicating Outlook cannot connect security to the server. Emails without attachments work fine. Some emails with attachments work fine (I haven't been able to determine if it's by file type, size, some combination, etc). I've contacted my ISP who indicates it's not their problem as I can send using their webmail application without problems. I've also been told by another who is having this same issue that they can send via Apple Mail with no problems. Thru experimentation, if I turn off Vulnerability Protection in the Firewall, the emails can be sent although it takes a lot longer to send. Reloading Norton Deluxe 360 doesn't fix the issue. Rebooting macOS into Safe Mode allows me to send the email without a problem but I believe the Firewall is being bypassed.
This is discussed in the following thread.
https://community.norton.com/en/forums/holds-emails-attachments-outlook-outbox
Anyone know of a Norton response this this? Still an active issue for me. I've done comparison tests with Outlook and Apple mail running on the same machine, both using N360 - Outlook will not send attachments whilst Apple Mail does....
How do we know that Norton has an active case on this?
I've spoken with Apple development engineers. After some lengthy troubleshooting, they indicate it's definitely not their issue. They indicate it's most likely a Norton issue. Their suggestion is to uninstall Norton as they feel macOS has ample safeguards in place.