This is the GTUBE -- the Generic Test for Unsolicited Bulk Email.
If your spam filter supports it, the GTUBE provides a test by which you can
verify that the filter is installed correctly and is detecting incoming spam,
in a similar fashion to
the EICAR anti-virus test file.
Spam filter developers should add a rule, where possible, to recognise
the following 68-byte string in the message body, and trigger on it:
Note that this should be reproduced in one line, without whitespace or line
breaks. A suitable mail message in RFC-822 format can be downloaded here.
This string and mail can be reproduced freely, without attribution; they
are hereby placed in the public domain.