This might indicate incorrect server settings. Or maybe a password issue. What ISP for your email? What settings for the account?

Well, the problem is resolved on its own just as it appeared it disappeared. I'm guessing it was with the CenturyLink mail server. CenturyLink has some strict (weird) filtering rules. We have a holistic nutrition practice here in NJ and occasionally a suppliers e-mails are blocked for some reason. I know that I can not send an e-mail with an anti-vaccine URL. --Thanks --Jim

I suggest you get a mail provider that is actually aware of how email works. Unfortunately that would appear to preclude all the ISP's and Microsoft (they only understand Microsoft).

If you are running a business, a business class of mail account is an essential these days. Consumer accounts, particularly in the USA, are simply not fit for more than casual use with the expectation of failure. There is the added advantage of consumers being more likely to read mail from a custom business domain.

This company has been mentioned in this forum a lot over the years, and I post the link to provide you with an indication of the cost of a business class email as opposed to using your consumer connection from the like of centurylink. There are many providers, most deliver what you pay for. I have no association with any of them (except as a customer) nor does the Thunderbird project. So this is not a recommendation.

I have this exact same problem. Just when it seems to have fixed itself, it comes back. I have checked the server settings and my password. All seems to be correct. What is the solution?

Well, CenturyLink (yes I'm stuck with them) says that I have malware on my laptop that is causing the problem! Taking them at their word, I ran my Norton clean-up tools and did a reboot and the problem went away??? Norton did not find any malware and this has worked several times. I have also noticed that Norton like to plug in their VPN service (they don't like the password on my AT&T homebase router) and it causes problems with several web-sites. A reboot usually clears the problems.

I find this to be both amusing and disturbing. I have been using e-mail since before most of you, reading this post, were born. There was a time when the internet was wide open and was self policed. End points that behaved badly were denied access. The routers and network entities were in the hands of responsible people who did not think that profit was their primary motive and open software was the best. May God have mercy upon us.

re : I have also noticed that Norton like to plug in their VPN service

Suggest you switch the Norton VPN off. I have Norton and the VPN causes all kinds of problems. Links you know are good end up opening other completely irrelevant good webpages. Also you might find that CenturyLink do not accept the Norton VPN.

Alternative if you really want to keep the VPN - see if you can enable the Split Tunnel feature for your email application aka Thunderbird. Split Tunnel feature lets you exclude the email application traffic from passing through Secure VPN. Good info here:

• https://support.norton.com/sp/en/uk/home/current/solutions/v137513095

Thanks, yes turning off Norton VPN seems to do the trick.

Interesting how a supposedly anti malware product keeps being identified as malware. I gave up and now only use windows defender. It has worked out ok so far. (not years yet so I am still a little apprehensive, but getting close)

Interesting how a supposedly anti malware product keeps being identified as malware. I gave up and now only use windows defender. It has worked out ok so far. (not years yet so I am still a little apprehensive, but getting close)

Hi Matt I'm using Norton 365 and it does work ok. But I had to switch off VPN as too many issues. I have also set up to allow scanning, BUT it must not attempt to fix, it must ask me what to do. This means if anything in Thunderbird gets flagged up, I can identify the file, stop the fix and then deal with it myself knowing which file has the problem. If an mbox file is identified - I can choose to save all emails in file as .eml files in a desktop folder I've called 'ScanFiles' - then scan that folder and this time it identifies a specific email which I can then delete and compact folder. Then delete all the .eml files and empty the computer 'Recycle Bin'. It sounds a bit long winded, but it's quite quick in reality and a lot less risky than allowing an auto fix.