web.de/gmx mailbox synchronization always fails

I tested eM Client a few months ago and bought it right away because of the great features. After migrating all my email accounts from Thunderbird, everything seemed to be working fine for a few days. However, with my main mail account at web.de, errors occurred more and more frequently when synchronizing the mailbox. Now the error messages keep appearing. I always get a red triangle after waiting for some time with the message: “The connection failed”. In this way, even emails have been lost over the period of use. eM Client shows the mails as an entry, but the entire content is gone. I then contacted the support. After a log analysis, he claimed that the problem was clearly with the provider. Apparently the web.de server simply stopped sending at some point. But that can’t be. it worked for a while. In addition, I can still access my mailbox with Thunderbird and the mail program on my smartphone without any problems. The web.de support said that the problem must clearly be with the mail program. Unfortunately, however, no support can be provided for mail programs from other manufacturers. Now I’m standing here between the fronts and nobody is helping me. I hope now that someone else has an idea.
I used eM Client version 9.2.1577. The whole thing runs on a Windows 10 latest version completely patched. Then I still have the GData AntiVirus running. I’ve checked the IMAP settings a thousand times. They’re fine.
Does anyone else have an idea? If log files are necessary, just let us know. Then I create some.
greetings from Germany

If you give the ticket number, I can look at what was in the logs.

Can you completely disable that and see if there is any difference.

Hello Gary,
Thank you for the feedback. The ticket number is: #150476.
I just deactivated the virus scanner’s email check and started eM Client. Now all mails could be fetched without errors. I’m a bit surprised about that. I had run this exact test before. That didn’t help. Oh well. Unfortunately, I cannot leave the virus scanner switched off. This is self-explanatory. But I will now involve GData support.
I still have to get rid of one thing. I still think the problem is with eM Client. We’ve tried a lot in the last few weeks. After the process of elimination, it can now only be eM Client. How else can you explain that Thunderbird has no problems with the same settings and an active virus scanner on the same computer. eM Client has to do something differently.
Greetings Andreas

It is because the security app is blocking eM Client.

Hello Gary,
I am not happy with this answer. I had already written that I would write to GData support. But that doesn’t change the fact that eM Client is still the problem here. It must be clear to you that the probability of finding the problem with the virus scanner is very low. Other mail programs have no problem synchronizing with the mailbox despite an active virus scanner (Thunderbird, Outlook). Only eM Client cannot do that. eM Client has to do something differently so that the virus scanner causes such negative effects.
Greetings Andreas

Hi gary,
I have new information about my problem. I have received feedback from GData. After a few small tests with different settings, they recommended that I switch off the virus check for SSL/TLS connections. Once I did that, I was suddenly able to sync all my mailboxes with no issues. Even if I don’t like this workaround, it makes it possible for me to finally use eM Client the way it wanted to be. Unfortunately, I don’t understand why we didn’t find this solution sooner. I’m sure you asked me to take the test, and I did. Back then, however, the result was not the same as it is today.

In this post, manu wrote that she had the same problem and pointed out that she had previously also imported the GData certificate into eM Client. I was not aware that this was necessary. In your reply email of November 9, 2022, I understood you to mean that eM Client automatically regulates the use of certificates. I therefore imported the GData root certificate into the Windows certificate store. Unfortunately without an improvement. Now that I imported the certificate into eM Client, there was an immediate improvement. Since then I can synchronize my mailboxes even if the virus check for SSL/TLS is activated again.

Conclusion: The problems described in my ticket were all caused by the faulty communication between eM Client and GData. Due to the missing certificate, eM Client could not handle the connection properly. However, you can also see from the ticket history that it never looked like the connection was not established at all. It was just so extremely slow that there were always timeouts. So I’m wondering why eM Client was even able to establish this connection without the certificate. Where is the error to be found here? However, as I have noticed in the last two days, the connection is not always reliable, even with the imported certificate. I suspect that the scanning process of the virus scanner simply takes too long, depending on the number of messages to be examined. I’ll keep watching.
Greetings Andreas