What causes undeliverable mail?
Sending email is a process that depends upon the interconnection between mail systems — and based on the logs we have seen concerning undeliverable mail, often multiple tries are necessary to interconnect (when, for example, the receiving system is down or busy, or the circuits are busy). When systems cannot exchange mail within a certain time — often several days, one of the systems may reject the mail, resulting in an “undeliverable mail” message. More often, the systems place the given piece of mail onto “low” priority — which can cause delays of several weeks before the mail emerges to be sent again. Sometimes a “fatal” error will occur because of a unique, one-time circumstance — and based on our logs this occurs with about 1 in 10,000 messages. More often, mail may be undeliverable for several hours or several days, due to circumstances with your provider. Based on our logs this occurs more than weekly.
