If you use eM Client with a Gmail account “and have external POP accounts configured online in your mailbox to arrive in your Gmail Inbox” where i personally had one i used to pickup, then you will need to remove that online in Gmail, and then “setup automatic forwarding from those other external account mailboxes” to forward to your Gmail account mailbox, or you won’t see those account emails in eM Client Inbox from January 2026 as per Google changes below.
Quote Extract from the above Google support page
“Starting January 2026, Gmail will no longer provide support for the following features:”
“Check mail from other accounts: Fetching emails from third-party accounts into your Gmail account, with POP, will no longer be supported”.