26,000 users

Changed Component to Documentation. Something like the following should be added to the docs on mass_contact.

Scaling factors:
-Retrieving userids and emails in a scaled way: no
-Sending email in a scaled way: yes, within server limits
-Keeping connections up while the long process continues: no

If the server has sufficient memory for holding all those email addresses in memory, mass_contact should have no problems with 26,000 users (~2 MB free should do it). I don't think 26,000 users pushes the envelope here.

There is a setting on the mass contact admin page (at /admin/build/mass_contact/settings) that allows you to break up the sending of emails into chunks so that you're not sending all 26,000 in the same message, which would probably choke most servers' sendmail programs. mass_contact relies on the drupal_mail function to actually send the email (in includes/mail.inc), which can use either the default php mail() function, or use some magic you can set up in smtp_libraries. Configuring smtp_libraries to farm out emails to a server farm is probably a job best left to the professionals.

Additional comments were added to the front page and a README.txt was added to the project. Hopefully that will cover this issue.