GTUBE
The GTUBE (Generic Test for Unsolicited Bulk Email) is a test string used to test anti spam solutions, notably those based on spamassassin. It is a 68 byte string, and by default it carries an antispam score of 1000, which would be sufficient to trigger any installation.
The contents of the string are as follows:
XJS*C4JDBQADN1.NSBN3*2IDNEN*GTUBE-STANDARD-ANTI-UBE-TEST-EMAIL*C.34X
And should be placed in the message body of a RFC822 compliant email message, without any linebreaks or whitespaces.
Note that there exist some varieties that might not be recognized by all filters, notably the NAItube (which will carry a variable weight) and the GTphish (which will trigger specifically as a phishingmail), which are used in the Mcafee implementation of spamassassin.
Source: http://spamassassin.apache.org/gtube/