Secondary Email Account (Non-zoho) doesn't show up in imap

Secondary Email Account (Non-zoho) doesn't show up in imap

For the longest time I forwarded emails from my other email Account to my zoho account. This resulted in errors over last months so I changed the setup to let zoho fetch the account over pop3. That was configured this way from day1 but practically overwritten by the other mail-provider forwarding all emails to my zoho address. This worked fine but since I deactivated the forward (in the other provides web interface) I cannot view my emails through imap anymore because they do not show up. The only way to see them is through the old web interface which seperates the two accounts.
But I'd like to see all my emails through Thunderbird and other mail programs through imap.

I'm using zoho for a long time now and I'd like to continue to do so. Especially since I have a 5 year Email Archive I probably are not able to export (The interface says emails of the last 12 months). But If I am unable to solve this quickly I would have to find another provider for hosting my emails. It'd be a shame though :-/