Since yesterday I've been having issues with the catch_all account.  It gets a lot of inbound mail, applies a forwarding filter to move out some genuine stuff (mis-spells of names etc), spam filters within Zoho and then what is left is grabbed by POP into gmail (much of which is then also filtered by gmail as spam too).

So just yesterday I cleared down the trash and spam folders in Zoho so they were empty, and this seemed to cause POP to work again.

But today, the same issue - Gmail reporting "Authentication error.  Server returned error "Mailbox locked."

I've been into the webmail client on Zoho, cleared down 5000 trash items and 10000 spam items and now the remaining items in the inbox (33 of them) were successfully grabbed via POP by Gmail.

I haven't had to manually clear down spam and trash before from Zoho, so is something going wrong?