Should we use a comma after “But” at the beginning of a sentence?
Usually, you wouldn’t use a comma after “but” at the start of a sentence. Because of their short length, coordinating conjunctions, such as “but” or “and,” naturally flow quickly into the main thought of a sentence. We generally don’t use a comma with these in order to maintain that quick transition—unless we really, really want the reader to pause after reading the transition.
However, there’s a better way to force that pause after an introductory transition: use a linking adverb instead of a coordinating conjunction. Linking adverbs, such as “however” or “on the other hand,” are longer words than conjunctions, and they do use a comma after them at the start of sentences, so they’re a more natural way to elongate transitional pauses.
For more information on linking adverbs, study this page: Linking Adverbs.