There have been many forum messages over the years regarding timeout errors reported by pop3 servers to email clients.
This post has a potential answer, and a question for further information, regarding a possible answer for some of these errors and messages.
I have Norton 360, Windows 8 and Outlook 2016, recently upgraded from Office 2013. I am getting intermittent but very frequent Outlook send/receive errors (I think originating about the time of the Outlook upgrade).
I have found, using WireShark network protocol trace, that the combination of Outlook and Norton 360 Email scanning has variable delays between the time that Outlook requests the next message from the pop3 server after finishing the receipt and processing of the previous message. I am using standard email on standard pop3 port 110.
There are many instances where this pause can be more than 6-7 seconds. In theory this shouldn't be a problem, just a bit annoying that it's a bit slow. However it seems to have uncovered a problem with my ISP's pop server because the ISP pop server has an inactivity timeout of about 7 seconds, which means that the pop server disconnects the TCP connection, therefore triggering a receive error in Outlook, and all the consequent error messages that appear in many other community forum messages.
The RFC standard for the pop3 protocol says that the inactivity timeout should be at least 10 minutes, so it would seem that my ISP is at fault with its pop3 server configuration. I wonder if many other ISP's also have a very short inactivity timeout which can be accidentally tripped by email clients and email virus scanning.
Anyway, I have an outstanding request to my ISP to assess and fix their inactivity timeout. However, it must be a worry that Norton 360 email virus scanning and Outlook between them can, on some days, take many seconds to scan a message (even tiny ones with no attachments), and on other days they can operate well within this 7 second deadline.
Does anyone have a clue as to why the processing time can be so variable, and why it is so slow?