When I encountered the sample sentence for 発信, I read this:
This reminded me of 配信 which I usually see online (especially on YouTube). How are these two words different?
Both 配信 and 発信 roughly mean "delivering the same information/message to many people".
配信 is used when:
発信 is used when:
For example, 配信 is done by Netflix, YouTube, a CDN, a mailing list system, etc. 発信 is done by a conventional radio station, an SOS radio beacon, a personal website, or even a fashion magazine.
In addition, 発信 also means "starting a phone call", in which case the antonym is 着信.
If the receiver is a single person/server, you can just use 送信.