Max PM recpients limit?

[BNL]

Some time ago I tried sending a daystart message to all players in my mini theme as well as my backup mod. However, an error was reported, I don't remember what is was anymore, but I assumed it was because I was sending it to too many people. I removed my backup mod from the send list and it sent fine, which had me assuming PMs can be sent to 13 people at a time at most.

However, I just received a PM that was sent to more than 13 people. Is there actually a PM send limit? What problem could I have actually encountered?