IMAP/SMTP troubles

Hello!
I have following problems with domain hosted with zoho - first one of mine usernames stop connecting to zoho from my phone/smtp clients - "user name or password is wrong" but there is no changes made by me. Few minutes later all my users was rejected by IMAP/SMTP servers of zoho with same error. So is this ZOHO issue?

This is secondary big issue here for 6 months since I use zoho to host my mails.