A long enough chat message can corrupt the protocol.

[purifetchi]

When you write a chat message close to the 64 character limit of classic, the server starts sending mangled packets completely corrupting the game for others.

Edit: Split the message after 64 bytes, the name prefix screws with the length.

[SepiaChiptunes]

currently a 64 character message breaks the protocol when sent:

CLIENT SENDS: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
SERVER CONVERTS TO: <koy>: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

so then, on the serverside the message needs to be split into x amount of variables
(example shown is python but you can easily reimplement variables from Py to C#)

message_variable_1 = "<koy>: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"
message_variable_2 = "> aaaa"

and send both the variables seperately back to the client(s):

CLIENT SENDS:    aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

SERVER CONVERTS TO: <koy>: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa

SERVER SENDS:       <koy>: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa
SERVER SENDS:       > aaaa

hope this helps!