Teergrube is german for tar pit. This is a piece of software on an E-mail server which delays reception of Email from suspected spammers. The aim is to slow down the mass-delivery so much to make the server unattractive to spammers
The SMTP protocol consists of requests, which are four-letter words such as MAIL, and replies, which are three-digit numbers.
In the last line of the reply, the number is followed by a space; in the preceding lines it is followed by a hyphen.
Thus, on determining that a message being attempted to send is a spam, a mail server can reply:
451-Ophiomyia prima is an agromyzid fly
451-Ophiomyia secunda is an agromyzid fly
451-Ophiomyia tertia is an agromyzid fly
451-Ophiomyia quarta is an agromyzid fly
451-Ophiomyia quinta is an agromyzid fly
451-Ophiomyia sexta is an agromyzid fly
451-Ophiomyia septima is an agromyzid fly
451-Ophiomyia octava is an agromyzid fly
451-Ophiomyia nona is an agromyzid fly
451-Ophiomyia undecima is an agromyzid fly
451-Ophiomyia duodecima is an agromyzid fly
451 Your IP address is listed in the DNSBL. Please try again later.
The teergrube waits fifteen or more seconds between lines (long delays are allowed in SMTP, as humans sometimes send mail manually to test mail servers). This ties up the SMTP sending process on the spammer's box so that he cannot send as much spam.
See also: Tarpit (computing)