Email reminders are kind of down and dirty and they will send the columns that are in your default report. Your real problem is that you need to fix the columns in the default report because I'm sure 300 columns are not relevant. So just go to settings, then reports, that at the top right there's a link for default report and you can take out a big machete and hack away at least 280 of those 300 default reporting fields.
In fact with 300 fields I would highlight them all remove them all, and on a curated basis add back the relevant ones.
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Mark Shnier (Your Quickbase Coach)
mark.shnier@gmail.com
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