I've got 2 email accounts configured on my domain hosted at Zoho. Both were working fine yesterday, but then I enabled two-step authentication, and my email client (Mail.app 7 on OSX Mavericks) wasn't connecting. 

After trying to connect via Google authenticator, I decided I couldn't be bothered configuring email access for two accounts on three devices (Macbook, iPad and iPhone). However, I found that there was a problem in that mail.app kept saying the username and password were incorrect for one of the accounts (the main admin account).

Here's what I've tried, to no avail:

1) Changing the password in zoho mail user settings

2) Changing the password in zoho domain control panel

3) Switching the account on and off in Mail.app

4) Deleting all zoho items in my mac keychain

5) Deleting the account in preference panes and reconfiguring

Given I have two accounts and one is working fine and the other isn't, I think this relates to the two-step authentication process; the account I managed to set up two-step authentication is the problem one, even though I've switched off two-step authentication for the whole domain. I wonder if there were a flag on the account somewhere which still thinks it needs two-step authentication, even though it doesn't?