This works fine in singleplayer though.

How are you sending the messages when chatNoOverride is enabled? (vanillaChat was replaced by chatNoOverride btw, so it no longer has any effect)

When I press tab, it switches between
">> Now chatting to minecraft <<" and
">>now chatting to #ircchannel<<"

It sends to the irc properly in single player but not multiplayer.

eirairc-mc1.7.10-2.8.215

chatNoOverride only works if some other mod overrides the chat and implements EiraIRC's ClientChatEvent API event. If there is no such other mod, then it will neither work on the client nor the server.

For completeness sake:

[23:43] BlayTheNinth huh, that's weird that it's working in singleplayer
[23:46] BlayTheNinth BBoldt: is asielib installed? that could be why it's working in singleplayer
[23:47] BBoldt I do have asielib actually
[23:49] BlayTheNinth the noChatOverride option relies on some other mod calling the ClientChatEvent for EiraIRC (or working around it in a different way, like the tab setup with TabbyChat)
[23:50] BlayTheNinth on the client side, asielib is doing it's own chat tweaks and in the process, calls an EiraIRC event that makes it relay IRC chat as normally
[23:50] BlayTheNinth but it's doing that on the internal server of the client
[23:50] BlayTheNinth in multiplayer, the client doesn't have an internal server that could call the event that the client-side EiraIRC needs to relay chat to IRC
[23:52] BBoldt is there any way I could make it behave like it does on singleplayer in multiplayer?
[23:54] BlayTheNinth Other than turning noChatOverride off (and thus making Aether II not work properly) or installing EiraIRC on the server and using the server-side bridge instead if you have access to it, no

Here, I made some videos to hopefully explain the issue better.

Maybe it should be noted that I have the aether mod installed, but I don't think that makes a difference unless you have special code for it or something.

Singleplayer (working perfectly, and doing exactly what I need it to!):
https://dl.dropboxusercontent.com/u/134976541/ShareX/2015-05/2015-05-18_14-34-15.mp4

Multiplayer(not working):
https://dl.dropboxusercontent.com/u/134976541/ShareX/2015-05/2015-05-18_14-35-51.mp4