is there an anti virus or other security software on the desktop that is perhaps absent from your other devices?

Note that there is a trend to the use of VPN's but I am yet to see one that works seamlessly with email. Most simply block the email ports however, providers like google check your geo location via IP address and tend to block access if your not where they think you should be. For instance a phone in California and a desktop connecting at the same time from New York.

Hi Matt.

Thanks for answering. My issue just got even more strange...

These are the symptoms so far.

On my mac, with no antiviruses and no software that constrains any connection...

Thunderbird stopped working some days ago. I have many accounts as I'm a web designer that also provides hosting, so I keep a copy of an email account of mostly every domain/web I design, so I can check customer's email behaviour.

These emails include gmail, domains from several hosters... so email is not the problem (and I can see these account through webmail!)... so I thought it was Thunderbird but....

I tried to set up one account in Mail app from Apple, and Mail does not detect my servers... crazy.

I think both issues are linked.

Surprisingly, I set up this account on Outlook for mac and it worked perfectly. Crazier

On my mobile (iphone) all my emails work fine.

So, my email clients on my mac do not work except for Outlook.

I'm installing an antivirus (my fault, I have never used one) to see whether there's some kind of software doing something strange in my computer...

What you say about google is very curious... it seems my computer is blocked, althoug I can navigate without issues.

This is by far the strangest issue I have found in my life.

What do you think?

Thanks!

I think look at your firewall, both any software one on your mac, but also any on your router.

I might suggest you try enabling dns resolution through SSL. Not a default configuration, but it fixed some issues I was having with both Firefox and Thunderbird related to DNS resolution.

General discussion for the Firefox implementation. https://support.mozilla.org/en-US/kb/firefox-dns-over-https

How to implement for Thunderbird. https://www.zdnet.com/article/how-to-enable-dns-over-https-doh-in-firefox/

Use option 2 about:config is accessed in Thunderbird via the config editor

Hi Matt.

Thanks for the tips. Not sure what dns resolution is, but I will read the articles.

I have narrowed my issue to my computer OS, as I don't have these issues in other computers. I have just installed Thunderbird on a windows laptop, connected to my router via wifi and I had no problems… so, it's something in my computer. I don't have a firewall nor I have enabled it….

Just a mistery to me.

I have given up by now.

If I ever discover what's going on, I will post it, just in case somebody else has this problems.

Thanks a lot for your tips.

BR

Enrique

when you ask for a web site say www.me.com, the very first thing that happens is a DNS request is sent out in plain text to the DNS server allocated to you. There are manual settings, but mostly the setting are automatic from your ISP.

The change I propose changes the DNS from it's own port (53 I think) to a request send on the same port as encrypted web traffic (443). Just the change of port can have a huge impact. It also side steps most of the net nanny type software however as they mostly rely on DNS snooping and poisoning for do their thing.

I NOTICED IN THE ONE EMAIL ACCOUNT THAT DOES NOT RECEIVE E-MAIL MESSAGES, ONE MESSAGE FROM THE HEALTHCARE MARKEPLACE CONTINUED TO E-MAIL THE SAME MESSAGE HUNDREDS OF TIMES ON THE SAME DATE AND SAME TIME. WOULD THAT BE THE PROBLEM WITH THAT E-MAIL ADDRESS AND HOW WOULD I FIX IT.

Ok guys... for who ever is listening to this issue, or having the same issue as me. I GOT T SOLVED thanks to Apple Support. It was nothing to do with Thunderbird. It was an OS X problem specific to my computer... I have to implement this solution EVERY TIME I start the computer btw.

Not sure why or how, but this is what I did, following a post by Apple Support

1) Create a New Location on System Preferences>Network>Locations (you can also go directly to this area by clicking Network Preferences right from Apple Menu) 2) Click Advance, then Proxies, then UN SELECT ALL (I had SOCKS Selected, and it gets selected again every time I turn on computer) 3) Go to DNS and delete what ever you have and add these ones: 8.8.8.8 - 8.8.4.4. - 1.1.1.1 - 9.9.9.9

Now my email works fine.

Sorry I do not upload screenshots as my menu is in spanish...

I have a possible alternative for you. It worked for me with dodgy DNS servers used by my ISP. It might work for you as it allows Thunderbird to bypass the traditional DNS in favor of using a link over HTTPS.

Use the config editor Locate the setting network.trr.mode set it to 2. once this is done. Locate the setting network.trr.uri. This will have defaulted to floudfare. Mozilla has an agreement with them about how little privacy they will invade with their logging. But you can use any of the provider in this list https://github.com/curl/curl/wiki/DNS-over-HTTPS#publicly-available-servers

In Options > Advanced > security use the "configure how Thunderbird connects to the internet." Settings button Set the proxy value to no proxy. The default is use the system proxy.

Those two things should I think do the same thing as your settings from apple do, except you will not have to set them over and over.