Avast Mail Shield is blocking IMAP email access in Mozilla Thunderbird

[sleepingvr4]

Avast's mail shield is blocking IMAP on Thunderbird.  As soon as I disable the mail shield Thunderbird works normally.

Is there a resolution to this?

[sleepingvr4]

This was read 213 times but not one person has any advise?

[DavidR]

I think this is because there is little information to work with.

A screenshot of the 'blocking' you are talking of might help.

In the meantime a search on 'Avast's mail shield is blocking IMAP on Thunderbird' returns many hits.

This was just one of them - https://support.avast.com/en-ww/article/91/#pc

[sleepingvr4]

I already tried to import the Mail Shield certificate and Thunderbird stated that cert was already in use.

And when I say block, I mean that Thunderbird is trying to connect to imap.gmail.com and it fails as long as the mail shield is enabled.

[Cluster-Lizard2014]

A long time ago I had something which sounds like a similar problem.

The trouble was not with AVAST or Thunderbird it was due to some update my email service provider (my ISP) had done. When I reported it to them, suggesting it was a certification issue, the problem was resolved a few days later without any explanation.

I suggest, if your ISP has a forum, you check there for anyone having similar recent trouble with Thunderbird or use other means of communication for problem reporting. Describe the issue, particularly the possibility of the involvement of the mail server certificate and AVAST's Mail Shield then maybe you'll get some joy.

You've reported it here so one of the likely party's involved is now aware there may be a certification recognition matter. So reporting it to your email service provider is the obvious next step.

But don't expect anyone to enlighten you as to what the problem was and who was to blame. Just hope that one or the other resolves it quickly.     

[Leo3487]

A long time ago I had something which sounds like a similar problem.

The trouble was not with AVAST or Thunderbird it was due to some update my email service provider (my ISP) had done. When I reported it to them, suggesting it was a certification issue, the problem was resolved a few days later without any explanation. 

LOL
The op said is gmail, no a ISP mail

[Cluster-Lizard2014]

Why do you think it matters who provides the email service?

By referencing that previous problem as I did it was actually making it clear that it was not Gmail being used in that case but it might be a similar issue.
   

[sleepingvr4]

I work for my ISP and we don't block anything.

When I originally started using thunderbird, i didn't have an issue and then one day after an Avast update i started to have to disable the mail filter to allow thunderbird to reach Gmail again.

[Cluster-Lizard2014]

Most ISPs do if you don't opt out of their default 'protection' packages, at least that is my experience.

I've not had any trouble with Thunderbird, both an older version I'm running on a VM and a fully up to date version but I wouldn't rule out that as the cause of your problem as the newer Thunderbird versions have not been trouble free.

It does look like AVAST is the most likely culprit in this case but good luck persuading them on that. I still think your most sensible course of action, now you've made them aware of a possible problem here, is to wait for the next AVAST version update and see if the issue remains.

[Nunzio77]

I recently installed Thunderbird with 3 IMAP accounts on a PC and didn't encounter any problems.
On my PC I use eM Client with IMAP and I don't encounter any problems.

[sleepingvr4]

Pushing this to the top.

I switched mail clients to eMClient to see if it made a difference.

Avast mail shield is still blocking IMAP.

[Nunzio77]

Pushing this to the top.

I switched mail clients to eMClient to see if it made a difference.

Avast mail shield is still blocking IMAP.

Very strange because I use IMAP with eMClient and I have no problem with Avast Free (latest version).
You should do a more thorough check.

Do you have the latest version of Avast?

[sva]

I have exactly the same issue, but with Hotmail and only when sending emails.    Back in July '22 I had (the same / a similar) issue, which was later fixed.   

Currently I use :

Thunderbird Client: 128.1.0esr (64-bit)

When Sending, it eventually times out with the error message:

"Sending of the message failed:
An error occurred while sending mail: Outgoing server (SMTP) error: The server responded: Timeout waiting for client input [..."

Turning off "Mail Shield" fixes this issue, though that's not really a fix...

Increasing the mail sending timeout within Thunderbird, has no impact.
Restarting Thunderbird in Troubleshooting mode, has not impact to this issue.

That said, the "new Windows Outlook" has no problem sending emails from the same account.

With Thunderbird, I have found, that if I hit "Cancel" then resend, then the message actually goes through.
I suspect it's a Thunderbird issue, though if there are Avast Logs which can I can use to help substantiate my suspicion to the Thunderbird Dev team, then please let me/us know where I can find them. Thanks.

[rocksteady]

Have you looked at this re Thunderbird & Hotmail/Outlook email? https://support.mozilla.org/en-US/kb/microsoft-oauth-authentication-and-thunderbird-202