[Mailman-Users] ISO RegExp example to block bot subscribe requests

[Woody Mon]

Hello, List is running on Mailman version 2.1.20.

Last several days began receiving hundreds of bot subscription requests (all gmail addresses).

All of format like:
blech+12345678 at gmail.com
zark+98765432 at gmail.com
etc.

I entered following regex lines in Privacy Options -> Subscription Rules -> ban_list

^.*blech
^.*zark
etc

Temporarily did the job, but the bot adapted and changed the prefix of the address string to:
crap+12345678 at gmail.com
grum+98765432 at gmail.com
etc.

Unable to keep up with the bots changing the address prefix.

Common to ALL of the bot subscribe requests is including the "+" symbol in the email address

So I tried entering RegExp ^.*+ but Mailman rejected this entry.

But was able to enter RegExp of ^.*/+
However that allowed all the bot spam requests through.

Can anyone recommend an example of a RegExp entry which would solve my dilemma?

Note: Unfortunately I do not have access to the server so unable to configure SUBSCRIBE_FORM_SECRET 

Thanks for any ideas.