The first entry in aSelection specifies the SMTP service entry that is to be used to send the email messages. aSelection may
contain only one entry ID. The SMTP MTM will append the Ids of all "ready" email messages which exist in the outbox that match
the IAP of the specified SMTP service. Whether an email message is "ready" is determined from its TMsvEntry::SendingState()const flag.
If an Internet connection has already been established by another client, then this function may fail with KSmtpNoMsgsToSendWithActiveSettings
if none of the messages specified in aSelection match the IAP currently in use.