The mailing list for listmasters using Sympa

[Matt Taggart <address@concealed>]

Hi sympa-users,

One of the lists we host has setup a web form on their website so people 
can enter their address and then get automatically directed to

https://listserver/www?list=listname&action=subrequest&email=foo%40bar.com&a
ction_subrequest=submit

which contains a button the user clicks to confirm submitting the request. 
When the button is clicked the address is emailed the confirmation request.

What we are seeing is that webcrawling spambots are able to enter an 
address in the form, submit, and then click the confirmation button. But 
they usually use a bad email address, so this results in the confirmation 
email bouncing to listmaster. We're seeing dozens of these a day.

Is there something we can do to prevent this? Maybe a captcha or some other 
way to exclude the spambots?

Thanks,

-- 
Matt Taggart
address@concealed