I am using Thunderbird to access 12 different mail accounts, 3 of them free zoho accounts.

I needed to reboot my PC and since then one of the zoho accounts now returns a ‘Mailbox Locked’ error whenever I try to read mail from that account. The other 2 zoho accounts work perfectly. (I have no idea if the zoho account was being accessed when I rebooted).

I have read the help section which states that this problem can occur when concurrent requests are made. I only use the Thunderbird client for pop access. I do however have additional access to the account via the zoho android app.

I have tried the following to try to solve the problem:

Logging out of the account on the android app.

Changed password. (In the hope of some form of account access reset).

Disabled POP on the account (Thunderbird error now returns ‘Service Unavailable’ as expected. Then re-enabling POP. (again in the hope of some form of account access reset).

I’ve tried not accessing the account at all for a few hours, hoping for a timeout.

It should be noted that I can quite happily send mail via the account.

I had expected that this error would clear itself, but as it hasn’t yet, can anyone help?