BB Software :: Regular POP3 Email Will Not Setup

My small business has recently moved to a new dedicated server and after working fine at first, I am now unable to set up any of our mailboxes on any BlackBerry device (tried Torch, Bold, Curve) on any carrier (Rogers, Bell in Canada and T-Mobile, AT&T in US). I try the basic setup (email address and password) and then when that fails, the advanced settings (which are necessary as my email username is non-standard; it is always username+example.com when the address is username@example.com and the mail server is mail.example.com). After a long "Processing..." I am told "Invalid email address and password. ... If the error persists, contact "my server" The thing is, all of these mailboxes works fine in any other email client with the same settings (Outlook, Thunderbird, iPad, etc) and as I said, worked fine a couple of times on BlackBerry before now not working at all. In a basic sense I am the administrator of my server, though I have been on with my hosting provider's support and they are baffled as well. This problem is not happening on any of their other similar hosted servers, just mine. whether there is some process, some address, something at RIM that must be permitted to communicate with my mail server tha could potentially be blocked somehow. My default mail server is Dovecot (including the BlackBerry "Fastmail" service, which worked fabulously before this started)