eMclient does not pick up emails directed to me at my btinternet address. I have several other email addresses and those show up pretty quickly in the separate Inboxes and the unified one… But the nbtinternet ones often turn up in the Inbox hours later - sometimes even days. Even more interesting, I find that Thunderbird picks up the btinternet emails just as quickly as all the rest. So saometimes I can read emails in Thunderbird that I can’t see at all in eMclient until much later. The settings must be OK bercause I do get them eventually.
I have several other email addresses and those show up pretty quickly in the separate Inboxes and the unified one. But the bt internet one often turn up in the Inbox hours later - sometimes even days.
As Thunderbird is receiving mail from BT Internet straight away but not eM Client till hours later or sometimes days later “on the same internet connection”, then that might be related to possibly “slightly different incoming mail server settings”, or could be possibly “something running locally resident on the computer” delaying mail arriving into eM Client that’s not affecting Thunderbird.
So if you can update what your BT Internet incoming mail “server address, port and security policy” is via “Menu / Accounts” so we can see if there is possibly any inncorrect settings in them.
Also if you are running any eg: Optionally installed Firewall / Security programs or Optionally installed Antivirus programs or VPNs “other than what comes default with your OS”, try completely disabling those to test incase of interference.