fails to authenticate with postoffice.net via imap

client works fine with gmail accounts
client fails to auth with netaddress.net (my usa.net account) which uses authentication on both imapd & smtp.
postoffice.net works fine under imap via default ipad client & k9 for android
ipad client displays port 587 for smtp.postoffice.net and port 993 for imap.postoffice.net (I think they autofilled)

I think it cannot be too complex, thunderbird instructions (changed email prefix) are as follows. Have tried a few times in the past year or so since using Postler 0.1.1 over Ubuntu Studio 12.04LTS

Go to the Tools menu and click on "Account Settings".
Click "Add Account"
Choose "Email Account".
Click "Next".
Follow the steps of the Account Wizard.
Under "Getting Started", fill in the following information:
Your Name: Your full name (e.g. John Doe).
Email Address: <email address hidden>
Type of incoming server: IMAP
Incoming Server: imap.postoffice.net
Incoming User Name: <email address hidden>
Account Name: Any name to identify the account (e.g. Net@ddress).
Finish the Wizard and then choose "Outgoing Server (SMTP)" from the menu on the left of the Account Settings Page.
Server Name: smtp.postoffice.net
Select the checkbox for "Use name and password".
User Name: <email address hidden>
For "Use secure connection", choose "No".
When finished, click "Ok".
When prompted to enter a password, type in the appropriate Net@ddress password.