@sunday9pm - I don't have a clear answer to your problem, but have some info for you.

> It's connected via ethernet to our old TPG supplied HUAWEI modem router HG659

> I'm not sure what NAT does or if I need it.

You definitely need NAT, but your HUAWEI modem router is doing that already. Your internet provider is giving you a single address on the internet, allowing for one device. NAT on a route (Network Address Translation), let's you have multiple private addresses in your local network (of the form 192.168.1.x), and the router translates messages as they go in and out from the public address to the internal private addresses.

You don't need this NAT function happening twice, both in the HUAWEI router and in your TP-Link.

I have the TP-Link X20, and that is how I have it configured. The two units are connected by ethernet to my Asus Router, and are configured as Wireless Access points, not as a router.

Sorry, but I don't know about getting back the virus control when in Access Point mode. I suspect your HUAWEI router may be doing home intrusion protection.

I hope this helps,

David

Thanks @DocDavid. The issue re-emerged even after putting the X60 into access mode, so I switched them back to router mode. I then noticed looking at the log files of macOS Mail that it is the IMAP sockets that don't seem to work ("0x0"), and a Google search suggested it may be a clash with IPv6, so switched that off. Again the problem re-emerged.

What I have now managed to do is put the Huawei into bridge mode (switch off its DHCP and NAT functions and only use the VDSL modem function). That requires me to re-configure the X60 to use a static IP 192.168.1.2 and PPPoE using my username/password for the TPG FTTB account. Fingers crossed, so far so good, it works!

@sunday9pm  - Glad you found something that looks like it may work.

The reason I found your post is that may Mac Laptop was not connecting to IMAP. All other network functions were working (e.g. web browsing, SMTP access). Like I mentioned, I have my Deco X20 in Access Point (AP) mode. I have not turned off the WiFi from my older Asus router, but have it with a different network name. On my Laptop, I switched to the Asus WiFi network, and everything worked. Then I switched back to the Deco WiFi and everything continued to work.  Puzzling. I'm guessing that just disconnecting from the Deco and reconnecting to the Deco is all that  would have been needed to clear up the problem.  Right now, things are working well.

Hi @TP-Link_Deco 

The outgoing SMTP mail servers were never an issue, they always remained connected. The issue was with the incoming IMAP connections, and it was not isolated to just one of them, but three different email providers: GMAIL, iCloud, and GMX.

Examples from the log files at the time the IMAP connections were disconnected:

iCloud

INITIATING CONNECTION Jul 20 20:52:20.708 host:p68-imap.mail.me.com -- port:993 -- socket:0x0 -- thread:0x600007cd4040
 

GMX

INITIATING CONNECTION Jul 16 23:54:49.605 host:mail.gmx.com -- port:587 -- socket:0x0 -- thread:0x6000075dfe80
 

GMAIL

INITIATING CONNECTION Jul 14 09:22:01.480 host:imap.gmail.com -- port:993 -- socket:0x0 -- thread:0x600007fce400
 

Quitting and restarting macOS Mail would fix the issue for a couple of minutes, but then the IMAP connections were dropped again. Same with a laptop restart. I think I have now permanently resolved the issue by reconfiguring the Huawei modem router to be in bridge mode (to connect to VDSL only), and the X60 uses PPPoE to connect to the Huawei modem. I suspect that the IMAP drop-out was related to a DHCP / NAT clash between the Huawei modem and the X60.

Hardware model and firmware version are listed in my original post:

Model: Deco X60

Hardware Version: V1

Firmware Version: 1.2.4

@TP-Link_Deco - you quoted an Apple support article in your message.  It is titled "Verify an email account’s outgoing server in Mail on Mac". The "outgoing server" connection is fine.  That is SMTP.  It is the incoming, or syncing connection that is having problems, the IMAP connection.

Like @sunday9pm , it was the IMAP connection, to both Gmail and to SBCGlobal, that was not able to connect.  The Apple Mail client makes connecting to Gmail very automatic, hiding the details of the connection configuration (port number, ssl, etc). It is just configured as a gmail connection.  Similarly, SBCGlobal is just configured as a Yahoo server, all automatically setup.

I have a Deco X20.  Firmware Version 1.2.4 Build 20200527 Rel. 46779 .

David

It appears the IMAP dropout issue is back... so switching the old Huawei modem router into bridge mode did not resolve the issue... 

My ISP fixed a modem issue; but the problem is still here.