I noticed that Thomas English Muffins are certified OU-d. I heard that one may not eat dairy bread. Am I allowed to eat the english muffins?
The Gemara (פסחים לו) explains that Chazal made an edict prohibiting one to make or eat dairy bread. The reason for the prohibition is the concern that one may forget that the bread is dairy, and end up eating the bread with meat.
The OU certified products that have a dairy symbol on them are not dairy. The OU takes the position that the bread products which they certify contain less than one part out of sixty from milk or other dairy ingredients. Therefore, the dairy in the bread is null and the bread remains pareve. Normally, one would be forbidden to nullify a forbidden ingredient in kosher food, and it is only permitted after the fact. However, there are two reasons why the commercial bread is different.
The first reason is that the non-Jewish factory is putting in the milk regardless of if a Jew wants it in or not. The factory is not nullifying the dairy on behalf of the Jew. The second difference is that the milk is a permitted food prior to being put in the bread, and was nullified as soon as it got mixed into the dough. Therefore, nullifying the dairy is not considered like nullifying a forbidden food.
Since the milk is halachically non-existent, the english muffins are permitted.