We have found recently that some iOS users are unable to ‘verify’ after updating account settings such as new password or correcting settings. The error usually is ‘smtp server not responding’. Or if it reverts to the original password, in the case of attempting to update the password, it may say ‘invalid username or password’ because it reverts after it gets the first error of ‘smtp server not responding’…
I have had about 4 cases where customers have brought the device into the office and in each case I was able to get it going by removing the existing IMAP Hay account. Then power off/on the device. Then re-add the account.
I’ve seen it happen with iOS 11, 10, and 9 so we do not seem to have any OS version pattern. At least we now know how to get it going.