Machines being down or overloaded may scramble the order in which a series of messages are sent. This is embedded in the protocol as a tradeoff to ensure messages get sent eventually. As a messaging protocol, SMTP is less concerned about sequencing. The issue arises when a transaction system is layered on top of the messaging capabilities. Hence the sender assumes that it went through if she doesn't hear anything to the contrary.
Some mail programs cooperate with each other.
Will usually get errors for few messages, mass message errors may not be sent back to sender. If we were to accept a more limited domain, are there alternatives to SMTP that are not LAN based. Keith handed out a Summary of Environments Constraints . The team reviewed the document and suggested the following additions and revisions. This may require a change in the team's charter.