According to C.TRAC information solutions of Strongsville, Ohio, the US Postal Service handles 6-billion "undeliverable as addressed" (UAA) pieces each year and results in slowed delivery, non-delivery, returned mail, and mail delivered to the wrong address.
"30% of all US mail contains addressing errors."
"Every year 32% people change their email addresses."
Undeliverable mail costs close to 1.8 billion dollars per year to process. Costs are passed back to mailers and consumers in the form of rate hikes.
Besides having a wrong e-mail address, non-delivery of e-mail relies largely on overcoming hurdles such as:
- Blacklisting - Certain domains and IP addresses are refused delivery by the recipient email server.
- Greylisting - The initial attempt to deliver is rejected, and subsequent attempts are accepted. This is particularly effective in the fight against spam as spammers typically only try once to send a mail.
- Tarpitting - The email system takes longer to accept each subsequent message, resulting in high volumes of mail to the same domain taking days to deliver.
- Throttling - The email server will only accept a certain number of simultaneous connections from any particular mail server
For more on e-mail non-delivery, click here or here.