Multiple Identities in Evolution

[Jim George <jg014a8950 blueyonder co uk>]

Folks,

although I can receive from multiple POP accounts and define multiple
SMTP accounts.  I only appear to be able to send from the default
account.

I get the message Mailbox Unavailable.

Can anyone tell me what I'm doing wrong? Or is this not an Evolution
problem at all?

TIA,

Jim