Are they POP accounts at 3 different providers / mail servers, or just 3 accounts at the same ISP/server?

What antivirus and other security / firewall software are you using?

In order to do a quick resolve, you could safely uninstall v 45.5 and reinstall the 45.4 version, assuming that 45.4 the previous installed version that worked (this can be checked in Options > Advanced > Update > Show Update History). If that works, chances are your security software just didn’t catch up properly. Also and first, please have a look at the Cannot send messages and Cannot receive messages articles.

Just in case, make sure Options > Advanced > Network & DIsk Space > (Connection) settings are not set to use a proxy in any way, unless you are required to use one by a system administrator.

The POP accounts are with 3 different providers.

Using Norton antivirus and firewall but still have problem with this turned off.

Tried going back to 45.4 but still not working on POP3, which it was working before 45.5 update

looked at the Cannot send messages and Cannot receive messages articles, but no help there

Changed Options > Advanced > Network & DIsk Space > (Connection) settings changed from 'Auto' to 'no proxy'.

I am still having a problem with POP3 accounts

Before focusing on Norton: do these 3 POP accounts happen to be hotmail or msn accounts?

Looking at and quoting Matt in this question showing some resemblance: "Check the firewall component that Thunderbird is allowed and the exact version number. My understanding is the the firewall is picky on version numbers. so for example 45.3 will work and 45.4 will not. For that matter 43.3.0 will work but 45.3.1 trips it up."

Therefor,

• Open the Error console in Thunderbird and note any similarities to what you see there. Then make sure to fix the firewall rule to accept the Thunderbird version as well as the ports.

If that doesn’t help: according to my info, Symantec / Norton products are only able to "intercept" traffic for POP and SMTP servers, not IMAP. Additionally, turning off an antivirusproduct does not guarantee things should work as if they were not installed at all. Point is, it should be Norton interfering.

Can you try to

• Disable Antivirus scanning in Thunderbird using Options > Security > Antivirus ?

Since that should work for incoming mails only but can rule out Thunderbird to be at fault there, please also

• Disable any Norton email scanning feature (while the product remains enabled) bot for outgoing and incoming connections, such as SONAR, Auto Protect etc.

If that doesn’t help, remove Norton entirely and reboot. If that helps, you can consider reinstalling it, but try enabling its features one by one if they are not set as such (and preventing connections) from that point.

All the POP3 accounts were with different ISP's, not Hotmail or MSN. I updated Thunderbird to 50.0b3 and turned off the advanced settings in Norton, my emails synced. I then gradually restarted the advanced settings in Norton, looking for the one causing the problem, but with Norton fully running, I appear to no longer have a problem with my emails, they are all getting through.

Thank you for your feedback, glad it’s working properly. Would you still like v 45.5 to work properly too, or rather leave it as it is?

Also, is 45.5 still installed? If so, you could run both versions in parallel (well, not at the same time as 50b, but using the same profile data like you appear to do now, unless you set up all acounts as new in a new profile) as long as Norton allows both versions in the firewall.

Main goal of course is to rule out any issue in TB 45.5 itself and find the real cause, i.e. we still don’t know if Norton now learned about the program change properly in a way it could do for 45.5 as well. It could be a caching issue for 45.5 - choosing Options > Advanced > Network & Disk Space > Clear now could fix it. However, assuming 50b uses the same profile, that would cause the issue to occur for any version. The only thing we do know is the change wasn’t picked up properly, though I’m not convinced it is a Norton issue. ^{(I wrote "Point is, it should be Norton interfering." above, but intended "Point is to prove it’s Norton interfering".)} I just think it should work for 45.5 now as well.

If you’d rather leave things as they are, that’s fine - could you mark your last post as solution then?

I have re-installed V45.5 and it appears to be working ok Not sure what was causing the problem