Up until a week ago I had the "notify me of new subscribers" option in my YouTube settings switched on, but recently I (and from what I hear a lot of people) have been inundated with several spam-bot accounts ghost-subbing (without actually subscribing, only sending the notification) with dumb usernames like "Sub to my channel or I'll unsub" several times a day, so I was forced to switch subscriber notifications off. All this means is that for REAL people who subscribe to me and want me to know you did, you have to leave a comment or message me. Inconvenient I know but that's how YouTube be right now.
My YouTube channel: https://www.youtube.com/user/mfsto
Trailer: https://youtu.be/f0mDNFxPeX4
Link
TailBit
If there is any logic to their names, then maybe you could set a email filter to get rid of most of them .. or maybe there is a software that can compare your sub list to see which new ones that stick around?