Did you know WorldClient has support for aliases?
Go create an alias (without wildcards), then hit the compose button in WorldClient and note that the FROM field is now a dropdown — You can choose to send mail using any alias which points to your mailbox.
Even better, when you reply to a message, WorldClient will automatically choose the alias to which the original message was addressed.
There is also a hidden INI switch that can influence this behavior,
WORLDCLIENT.INI, [Special] section.
UseFirstAlias=No (or Yes)
If this is set to yes, WorldClient will always use the first alias which applies to a mailbox (not counting wildcard aliases) rather then guessing at which alias is most appropriate.