OE has a box which can be checked to require a password to send mail. Have been unable to locate procedure for setting this in TP.
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Smtp requires authentication - how to
It's the same place it is in standard TB. Tools - Account Settings - Outgoing Server (SMTP) - Select Account - Edit. You'll see all the security options in there.
Can select which smtp from list but no opportunity to enter user & password. Am I missing a plug-in?
Setting the username is also in account settings, but you need to select the outgoing server option rather than picking a certain account. The password is stored in the password manager (tools - options - privacy). It will automatically prompt you for it and offer to store it when you send your first email.
This is just like regular TB... the portable version is no different. For more details on how TB works, please check out the standard TB help files. You can find them from the TB Portable support page under General TB Issues.