Does the web server have permission to talk to the mail server? --> YESDoes the second account have permission to use IMAP? --> YESIs the second email actually an account, and not a shared mail box? --> ACCOUNTWell, I solved that problem.It was username issue:email.one@[deleted] --> works well with USERNAMEemail.two@[deleted] --> doesn't work with USERNAME, but with DOMAIN\USERNAME worksIt is very weird for me because there's no difference between those two Exchange accounts and AD users.