New Accounts under reseller email problems

[dynamicwebs]

My new accounts under my reseller account are all having problems sending and receiving emails. The problems intermittent and change from day to day. For the most part though the errors say that user authentication is enabled and this is not true. All settings are configured properly on the email clients. Again, these issues are popping up for every reseller account created.

I was hoping someone would be able to help out my isp figure this one out. The problem only exists on one of their servers. My other reseller account is just fine.