Yahoo Ports

http://www.helpbytes.co.uk/yconnect.php
Ports Yahoo! Messenger uses!
Client Access is where your PC initiates the connection, sends a request, and receives replies.
Server Access is where you PC takes requests from another system or systems.
Standard Connection & Yahoo! Chat
Port TCP80 (HTTP): Client access to Port 80 to receive roomlists, and insider news.
Port TCP5050: Client access for the Yahoo! Messenger & Yahoo! Chat connection.
File Transfer
Port TCP80 (HTTP): Server & Client access to Port 80 to share files. If this is a problem (you already run webserver) you can change to another appropriate port.
Voice Chat
Port UDP/TCP5000-5010: Client access to Ports 5000-5010. If UDP access fails, it will try TCP. So enable both.
Webcam
Port TCP5100: Client access to Port 5100 to receive webcams. Server access on Port 5100 to allow p2p cam sessions may be required.
P2P Instant Messages
Port TCP5101: P2P instant messages may occur. For this, server access on Port 5101 is required!

Firewall Users
If you use a firewall, local, or if you connect through one remotely, you will need to make sure the appropriate connections as listed above are all enabled on the firewall, otherwise Yahoo! Messenger will not connect. Yahoo! do have a list of servers, but it would be more appropriate to allow the connections on any servers, as they constantly change their server list.
Yahoo! Messenger may be seen on the firewall as ypager.exe because this is its original, and internal name.

Proxy Users
You can connect to Yahoo! through a HTTP proxy (this is slow and really unreliable) or SOCKS4 and SOCKS5 proxies (much better). You just set the server, username and password (or bits necessary) on the appropriate tab.
There are two main reasons you may use a proxy:
Firstly they offer anonymity, they keep your IP address etc… hidden.
Secondly it’s the only option perhaps in the workplace.
Proxy connections used for anonymity cost the user, such as at The Proxy Connections who offer SOCKS5 access for Yahoo! Messenger.
Proxy connections used in the workplace will require usernames and passwords off the admin, who may block IM usage, these will not add anonymity, and remember your workplace may log your actions*.

Routers
If you use a highspeed connection, it’s possible you use a router to distribute/share your connection between PCs. This is not a problem for your standard connections, but is for servers.
If you are to act as a server, the router needs to know which PC to send the requests too.
Using the information above, “Ports Yahoo! Messenger Users”, set the appropriate port forwarding.
That is, you need the IP of your PC as on the network, and forward requests to the services you use (such as if you use file transfer) to that IP, by entering the port and your IP (for example for filesharing, port 80 -> your network IP).

Routers and Port Triggering
Yahoo! Messenger may make a connection on a port X to a Yahoo! server, and receive a reply to a port Y. This is a problem to your router, it doesn’t know which PC on the network to send the request to. Port Triggering is a system by which you tell it if the Application (Yahoo! Messenger) makes a outgoing request on port X, any incoming connections on Port Y are for that application (Yahoo! Messenger) to handle.
You might need to set this up for voice chat as it uses different ports as listed above, p2p IMs and Super Webcam.
WebHazard has a graphical example on how for the linksys router and Yahoo! Voice chat! View that Here!
Linksys has an example on how for their linksys router and Yahoo! Super Webcam! View that here!