What are the maximum message size limits for a Syslog source?

For Syslog the message size will depend on the protocol used for the Syslog Source.

The Collector by default supports UDP messages up to 2048 bytes. To increase the UDP message length limit to the maximum datagram size (64KB), you can add the following configuration to collector/config/collector.properties and restart the Collector:

collector.syslog.udp.readBufferSize = 65535

With the TCP protocol the default max message size the Collector supports for a single-line TCP message is 64KB and cannot be further increased.