I see that a long time has passed and no one answered this, so for this user and everyone else having this issue (which appears not to be that common and that indicates most people RTM) I will:
I'd like to clarify that I'm writing this as someone who has used the system quite extensively, and has read all the documentation. I have no knowledge of the sg source code. If I mess up in some part, please let me know.
In this case in particular that you mention the
us is being interpreted as a max message count of 20 and not as a watchword.
Watchwords must be included into the "SOMEWORD" (as it is called everywhere in the sg documentation) and not be separated by a period/full stop. Example: with a watchword set to JOHN a correct address would be
helloJOHN.3.spamcowboy@spamgourmet.com
Unless you start using a prefix, there can only be a maximum of two periods/full stops in any correct disposable address. Before January 3 2002, this meant that all correct addresses should have two periods in it (and
only two periods if I'm not mistaken): the first period is interpreted as separating the "SOMEWORD" from the starting message count, and the second as separating the username. Example:
hello.3.spamcowboy@spamgourmet.com
According to the FAQ, as of January 3 2002 (and this is where your problem kicks in):
"you can use a word instead of a number -- the system will look at the first letter of the word and use its position in the English alphabet as the number" [...] "The limit of 20 still applies, so letters after 'T' will still count as 20. So, now: iam.a.spamcowboy@spamgourmet.com will be good for one message - 'a' being the first letter of the English alphabet" [...]
Hence, the U in your
us is taken into account as a 20 message count, and not as a watchword.
And as of "sometime later" of January 3 2002: If there is only one period included, it is interpreted as separating your "SOMEWORD" from your username; and the address will use the default number of messages. Example:
hello.spamcowboy@spamgourmet.com
Source:
https://spamgourmet.com/index.pl?printpage=faq.html