As you have redacted the server name, it is difficult to say if it is a known problem.
I do know that seznam.cz does not support IDLE (PUSH) IMAP, which is what eM Client uses. So in that case the messages will not be synced automatically.
Maybe this is a similar problem with your server. You could contact them and ask.
I have checked this with the email provider and it is not because of the server. Other mailbox works fine, only mine has an issue, additionally it does the same on two computers
Check the settings of the account (mailbox) that is working. Make a note of which port and security policy is being used. Go to the account that is not working and make sure you have the same settings.
If one account on the server works fine, but another doesn’t, and they have the same settings in eM Client, then I would check with the provider again. If you have the same server, the same settings, but only one is working . . . that most probably has to do with the server config of the account.
You still did not give the provider’s name. Sometimes free email servers have issues and the support is not always qualified or enthusiastic to solve them.
I can say that push IMAP works fine on 11 mail servers I use, three of these non-Gmail. I see the messages within some seconds of actual receipt. The delay might be a bit long compared to another email app; I haven’t seen a configuration for push interval, but in any case this shouldn’t affect that you can see the update.
Good fortune, and seems Gary Curtin has the best advice.
Yeah, I don’t know what that delay is all about, but I noticed it on test machines where other email clients will announce the new message before eM Client does. But just a couple of seconds, so not much of a problem.
There is no way to configure IDLE __IMAP on eM Client as the application waits for the server to announce the new message. Another type of IMAP, which eM Client does not support, has a configurable poll option. That is what is needed for seznam.cz, and why eM Client does not automatically get new messages when using that provider.