This discussion seems colored to me, I think by the likelihood that all prior participants are Catholic and know all about their Mass. Allow me to offer a non-Catholic viewpoint. When I see the word “mass” it does not signal any religious context to me. I read it as a general gathering of some objects or persons, or as a measure of the gravitational attraction of a body. I much prefer the use of Mass when referring to the Catholic event. It makes the word far less ambiguous. Seeing it capitalized immediately tells me that we are talking about a Catholic Mass – or possibly Massachusetts, but that is a different issue.
From the secular point of view, what you are celebrating is a Catholic Mass, a specific, named event, and with the use of “Mass” alone, the “Catholic” is implied. I noted one participant who was correct in that a Mass is a general sort of term, not referent to any particular named Mass, e.g. we usually capitalize the Superbowl but not the Football Game.
But the two examples are not equivalent. In my opinion the Superbowl is an inconsequential unimportant event. A Catholic Mass can hardly be considered inconsequential or unimportant. To me, the use of lowercase “mass” in referring to it rings of disrespect. Religion in general requires other exceptions to capitalization convention. When a writer uses “God” it means something entirely different from “god” – I think everyone would agree on that. “God” is a named entity, and therefore a proper noun. But what about the standard use of “He” or “His” (or “She” if the author leans that way) in referring to God? It is a sign of respect, I think.
I came here looking for the official rules from the Catholic perspective but there seems to be some disagreement. I am a writer; for the nonce I shall use “Mass” in my writing when referring to a Catholic Mass, for the purpose of clarity.
I often refer to the Church, so my finding this forum was welcome. When I write “the Church” it generally means a specific church organization, often Catholic. Again, in “the Church” we are talking about a specific named body. A “church” is just a building that happens to be used for a specific purpose. If the article is about the Catholic Church, then the “Catholic” is implied. When writing in this forum “Church” certainly implies “Catholic Church.” It seems a similar usage to me.