noun
source of a transmission; point of origin
Used for the origin of signals, broadcasts, or communications; often technical or journalistic.
警察はその通報の発信源を特定した。
The police identified the source of the report.
この情報の発信源は信頼できる。
The source of this information is reliable.
送信元 is more technical for the sender of data or messages, often used in IT contexts.
Compound of 発信 (transmission) and 源 (source, origin).