If people subscribe to our events (seminar day, symposium...), I want to exclude them from further reminder mailings.

I added a custom field check box to the Contacts module. If checked, I want to use that value to exclude them from the mailing list using a segment.

Problem: this field is not showing up in my criteria to segment.

What am I doing wrong here? Did I add he check box to the wrong module? Something to do with the box settings? Am I missing something in the segmentation part?

Thanks in advance!

Stijn