Are you *attaching* an .ics to a mesage in AquaMail?
Is the .ics generated on the fly -- i.e. are you doing some sort of "share event" from this Calendar app?
Calendar events can be sent as text/calendar parts, not attachments, but marked as "alternative" to text/plain and text/html. In other words, in a MIME message, they look like just one more type of textual content.
Since I don't have this calendar app and won't know what to do, can you send me a sample message to kmansoft / gmail, and answer my above questions along the way, please.